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.

2 files changed, 4 insertions, 3 deletions

diff --git a/mysys/array.c b/mysys/array.c
index 07abc460de7..e8b253a9e99 100644
--- a/mysys/array.c
+++ b/mysys/array.c
@@ -138,8 +138,9 @@ void *alloc_dynamic(DYNAMIC_ARRAY *array)
                                         array->size_of_element,
                                         MYF(array->malloc_flags | MY_WME))))
         DBUG_RETURN(0);
-      memcpy(new_ptr, array->buffer,
-             array->elements * array->size_of_element);
+      if (array->elements)
+        memcpy(new_ptr, array->buffer,
+               array->elements * array->size_of_element);
       array->malloc_flags&= ~MY_INIT_BUFFER_USED;
     }
     else if (!(new_ptr=(char*)
diff --git a/mysys/my_alloc.c b/mysys/my_alloc.c
index 5bfcb455b8a..d67b8be9bb8 100644
--- a/mysys/my_alloc.c
+++ b/mysys/my_alloc.c
@@ -461,7 +461,7 @@ char *strmake_root(MEM_ROOT *root, const char *str, size_t len)
 void *memdup_root(MEM_ROOT *root, const void *str, size_t len)
 {
   char *pos;
-  if ((pos=alloc_root(root,len)))
+  if ((pos=alloc_root(root,len)) && len)
     memcpy(pos,str,len);
   return pos;
 }