garray: Update NULL termination after copying array content

ptr_array_new(len, ., TRUE) ensures that there are at least len+1
elements in pdata, and that pdata[0] is null, but leaves the rest of
pdata uninitialized. After copying the array data into pdata[1] to
pdata[len-1] inclusive, we still need to make sure pdata[len] is a
null terminator.

Note that if len is 0, then pdata is not guaranteed to be non-null. If
it's null, then we can't add null-termination to it until its size
is updated.

Resolves: https://gitlab.gnome.org/GNOME/glib/-/issues/2877
Signed-off-by: Simon McVittie <smcv@collabora.com>

glib/garray.c

@@ -1387,6 +1387,9 @@ ptr_array_new_from_array (gpointer       *data,
       memcpy (rarray->pdata, data, len * sizeof (gpointer));
     }
 
+  if (null_terminated && rarray->pdata != NULL)
+    rarray->pdata[len] = NULL;
+
   rarray->len = len;
 
   return array;