MDEV-22387: Do not violate __attribute__((nonnull))

This follows up commit
commit 94a520ddbe39ae97de1135d98699cf2674e6b77e and
commit 7c5519c12d46ead947d341cbdcbb6fbbe4d4fe1b.

After these changes, the default test suites on a
cmake -DWITH_UBSAN=ON build no longer fail due to passing
null pointers as parameters that are declared to never be null,
but plenty of other runtime errors remain.

1 files changed, 6 insertions, 2 deletions

diff --git a/sql/field.cc b/sql/field.cc
index bdaaecc2026..fbce8b9041d 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -8446,7 +8446,10 @@ int Field_blob::cmp_binary(const uchar *a_ptr, const uchar *b_ptr,
   b_length=get_length(b_ptr);
   if (b_length > max_length)
     b_length=max_length;
-  diff=memcmp(a,b,MY_MIN(a_length,b_length));
+  if (uint32 len= MY_MIN(a_length,b_length))
+    diff= memcmp(a,b,len);
+  else
+    diff= 0;
   return diff ? diff : (int) (a_length - b_length);
 }
 
@@ -8503,7 +8506,8 @@ uint Field_blob::get_key_image(uchar *buff,uint length, imagetype type_arg)
     length=(uint) blob_length;
   }
   int2store(buff,length);
-  memcpy(buff+HA_KEY_BLOB_LENGTH, blob, length);
+  if (length)
+    memcpy(buff+HA_KEY_BLOB_LENGTH, blob, length);
   return HA_KEY_BLOB_LENGTH+length;
 }