fix appimage for systems with old Qt

[milianw]

Describe the bug
apparently the appimage breaks on systems that don't ship with Qt 5.10 or higher?

To Reproduce
try to run the appimage on an older ubuntu lts to check

Expected behavior
it should work

[milianw]

 » ./hotspot-v1.2.0-x86_64.AppImage
/tmp/.mount_hotspo6QWdJO/opt/lib/x86_64-linux-gnu/libexec/hotspot-perfparser: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.10' not found (required by /tmp/.mount_hotspo6QWdJO/opt/lib/x86_64-linux-gnu/libexec/hotspot-perfparser)
"The hotspot-perfparser binary exited with code 1 (TCP socket error)."

but I failed to reproduce that issue on a ubuntu 16.04 system

[0x6e]

Note that I only get the message after I attempt to open a perf.data file. The AppImage runs, but fails to parse the data file.

 » ./hotspot-v1.2.0-x86_64.AppImage
// Open a perf.data file
/tmp/.mount_hotspoQ9HXY2/opt/lib/x86_64-linux-gnu/libexec/hotspot-perfparser: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: version `Qt_5.10' not found (required by /tmp/.mount_hotspoQ9HXY2/opt/lib/x86_64-linux-gnu/libexec/hotspot-perfparser)
"The hotspot-perfparser binary exited with code 1 (TCP socket error)."
^C

 » dpkg -S /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
libqt5core5a:amd64: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5

 » apt show libqt5core5a
Package: libqt5core5a
Version: 5.9.5+dfsg-0ubuntu2.1

 » lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.3 LTS
Release:	18.04
Codename:	bionic

[milianw]

LD_PRELOAD and QT_PLUGIN_PATH are apparently both not set

[0x6e]

 » set | grep "LD_*"
OLDPWD=/home/0x6e
signals=( EXIT HUP INT QUIT ILL TRAP ABRT BUS FPE KILL USR1 SEGV USR2 PIPE ALRM TERM 16 CHLD CONT STOP TSTP TTIN TTOU URG XCPU XFSZ VTALRM PROF WINCH POLL 30 SYS ZERR DEBUG )

 » set | grep "QT_*"
QT4_IM_MODULE=xim
QT_ACCESSIBILITY=1
QT_IM_MODULE=ibus```

[milianw]

the 1.2 appimage is broken, continuous build works fine.