Bug#26911453 UBSAN ERROR ON SETRINGORDERTEST.SETRINGORDERCCW UNIT TEST

Fix misc UBSAN warnings in unit tests.
To repeat:
export UBSAN_OPTIONS="print_stacktrace=1"

./runtime_output_directory/merge_large_tests-t --gtest_filter='-*DeathTest*' > /dev/null

unittest/gunit/gis_algos-t.cc:78:70:
runtime error: downcast of address 0x000012dc0be8 which does not point to an object of type 'Gis_polygon_ring'

include/sql_string.h:683:35: runtime error: null pointer passed as argument 2, which is declared to never be null
    #1 0x373e7af in histograms::Value_map<String>::add_values(String const&, unsigned long long) sql/histograms/value_map.cc:149
    #2 0x294fcf2 in dd_column_statistics_unittest::add_values(histograms::Value_map<String>&) unittest/gunit/dd_column_statistics-t.cc:62

runtime_output_directory/merge_keyring_file_tests-t --gtest_filter='-*DeathTest*' > /dev/null

plugin/keyring/common/keyring_key.cc:82:57: runtime error: null pointer passed as argument 2, which is declared to never be null

Change-Id: I2651362e3373244b72e6893f0e22e67402b49a52
(cherry picked from commit 1fe3f72561994da1d912a257689e1b18106f8828)

include/sql_string.h

@@ -679,7 +679,8 @@ class String
     char *ret= static_cast<char*>(alloc_root(root, m_length + 1));
     if (ret != NULL)
     {
-      memcpy(ret, m_ptr, m_length);
+      if (m_length > 0)
+        memcpy(ret, m_ptr, m_length);
       ret[m_length]= 0;
     }
     return ret;

plugin/keyring/common/keyring_key.cc

@@ -79,7 +79,8 @@ void Key::store_field_length(uchar *buffer, size_t *buffer_position, size_t leng
 
 void Key::store_field(uchar *buffer, size_t *buffer_position, const char *field, size_t field_length) const
 {
-  memcpy(buffer + *buffer_position, field, field_length);
+  if (field_length > 0)
+    memcpy(buffer + *buffer_position, field, field_length);
   *buffer_position+= field_length;
 }
 

unittest/gunit/gis_algos-t.cc

@@ -66,15 +66,15 @@ void SetRingOrderTest::set_order_and_compare(const std::string &s1,
   wkt.set(s1.c_str(), s1.length(), latincc);
   wkt2.set(s2.c_str(), s2.length(), latincc);
 
-  Gis_polygon_ring *ringp= static_cast<Gis_polygon_ring *>
+  Gis_line_string *ringp= static_cast<Gis_line_string *>
     (geometry_from_text(wkt, &str, &buffer));
   DBUG_ASSERT(ringp->get_geotype() == Geometry::wkb_linestring);
   Gis_polygon_ring ring(ringp->get_ptr(),
                         ringp->get_nbytes(), my_flags, 0U);
   EXPECT_EQ(ring.set_ring_order(want_ccw), false);
 
 
-  ringp= static_cast<Gis_polygon_ring *>(geometry_from_text(wkt2, &str2,
+  ringp= static_cast<Gis_line_string *>(geometry_from_text(wkt2, &str2,
                                                             &buffer2));
   DBUG_ASSERT(ringp->get_geotype() == Geometry::wkb_linestring);
   Gis_polygon_ring ring2(ringp->get_ptr(),
@@ -155,7 +155,7 @@ TEST_F(SetRingOrderTest, RingDegradedToPointTest)
   std::string s1("linestring(0 0, 0 0, 0 0, 0 0, 0 0)");
   wkt.set(s1.c_str(), s1.length(), latincc);
 
-  Gis_polygon_ring *ringp= static_cast<Gis_polygon_ring *>
+  Gis_line_string *ringp= static_cast<Gis_line_string *>
     (geometry_from_text(wkt, &str, &buffer));
   DBUG_ASSERT(ringp->get_geotype() == Geometry::wkb_linestring);
   Gis_polygon_ring ring(ringp->get_ptr(),