Core crash after syncing a Mixed list.

[sync-by-unito]

While testing E2E cloud sync we stumbled on a crash when trying to sync Realm lists of Mixed type. Nikola pointed that there is a fixme in the execution trace code. Here is the stack trace for such crash:

/Users/clemente.tort/realm-java/realm/realm-library/src/main/cpp/realm-core/src/realm/sync/changeset_encoder.cpp:386: [realm-core-11.0.0-beta.1] Assertion failed: cx.w[1] == 0
!!! IMPORTANT: Please report this at https://github.com/realm/realm-core/issues/new/choose

            * beginning of crash

Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 829 (roidJUnitRunner), pid 798 (io.realm.test)

---

Build fingerprint: 'google/sdk_gphone_x86_64/generic_x86_64:10/QSR1.200715.002/6695061:userdebug/dev-keys'
Revision: '0'
ABI: 'x86_64'
Timestamp: 2021-03-15 16:55:00+0100
pid: 798, tid: 829, name: roidJUnitRunner >>> io.realm.test <<<
uid: 10144
signal 6 (SIGABRT), code 1 (SI_QUEUE), fault addr -------
rax 0000000000000000 rbx 000000000000031e rcx 000070f095e5c3f8 rdx 0000000000000006
r8 000070efba774f00 r9 0000000000000000 r10 000070efba774780 r11 0000000000000246
r12 000070efba774f00 r13 000070f007439b37 r14 000070efba774808 r15 000000000000033d
rdi 000000000000031e rsi 000000000000033d
rbp 000070efba774f60 rsp 000070efba774778 rip 000070f095e5c3f8
backtrace:
#00 pc 00000000000943f8 /apex/com.android.runtime/lib64/bionic/libc.so (syscall+24) (BuildId: b5c6019a3b4ea61b5e9a2f56319b584e)
#1 pc 0000000000097146 /apex/com.android.runtime/lib64/bionic/libc.so (abort+182) (BuildId: b5c6019a3b4ea61b5e9a2f56319b584e)
#2 pc 0000000000f64015 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (please_report_this_issue_in_github_realm_realm_core+5) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#3 pc 0000000000f6415e /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::util::terminate_internal(std::__ndk1::basic_stringstream<char, std::__ndk1::char_traits, std::__ndk1::allocator>&)+318) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#4 pc 0000000000f64228 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::util::terminate(char const*, char const*, long, std::initializer_listrealm::util::Printable&&)+168) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#5 pc 0000000000c04dcb /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::sync::ChangesetEncoder::append_value(realm::Decimal128)+123) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#6 pc 0000000000c049d5 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::sync::ChangesetEncoder::append_value(realm::sync::instr::Payload const&)+389) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#7 pc 0000000000c04733 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (ZN5realm4sync16ChangesetEncoder17append_path_instrIJRKNS0_5instr7PayloadERKjEEEvNS0_11Instruction4TypeERKNS3_15PathInstructionEDpOT+163) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#8 pc 0000000000c056d9 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::sync::ChangesetEncoder::operator()(realm::sync::instr::ArrayInsert const&)+57) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#9 pc 0000000000c40d52 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (void realm::sync::SyncReplication::emitrealm::sync::instr::ArrayInsert(realm::sync::instr::ArrayInsert)+98) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#10 pc 0000000000c40c4b /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::sync::SyncReplication::list_insert(realm::CollectionBase const&, unsigned long, realm::Mixed)+539) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#11 pc 0000000000e4dd10 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::Lstrealm::Mixed::insert(unsigned long, realm::Mixed)+336) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#12 pc 0000000000e4f5a7 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (realm::Lstrealm::Mixed::add(realm::Mixed)+87) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#13 pc 00000000008c4790 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (void realm::List::addrealm::Mixed(realm::Mixed)+80) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#14 pc 00000000007ae23c /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (ZZN5realm4List3addIRNS_4util3AnyENS_5_impl19JavaAccessorContextEEEvRT0_OT_NS_12CreatePolicyEENKUlS9_E_clIPNS_5MixedEEEDaS9+92) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#15 pc 00000000007ada22 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (ZN5realmL14switch_on_typeINS_3ObjEZNS_4List3addIRNS_4util3AnyENS_5_impl19JavaAccessorContextEEEvRT0_OT_NS_12CreatePolicyEEUlSB_E_EEDaNS_12PropertyTypeEOS9+354) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#16 pc 00000000007ad7db /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (ZNK5realm4List8dispatchIZNS0_3addIRNS_4util3AnyENS_5_impl19JavaAccessorContextEEEvRT0_OT_NS_12CreatePolicyEEUlSA_E_EEDaSB+59) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#17 pc 00000000007ad5b7 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (void realm::List::add<realm::util::Any&, realm::_impl::JavaAccessorContext>(realm::_impl::JavaAccessorContext&, realm::util::Any&&&, realm::CreatePolicy)+231) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#18 pc 00000000007a9e91 /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so ((anonymous namespace)::add_value(_JNIEnv*, long, realm::util::Any&&)+81) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)
#19 pc 00000000007ac26e /data/app/io.realm.test-1ZkeAM7SK_1mGLrGWrlPAA==/lib/x86_64/librealm-jni.so (Java_io_realm_internal_OsList_nativeAddMixed+94) (BuildId: 0b8931cff4a3dd0545ae6187a371eb9cb8f59b6d)