6886868: giflib has a memory leak in the MakeMapObject() function

Summary: free() the object before returning NULL
Reviewed-by: art, dcherepanov

src/share/native/sun/awt/giflib/gifalloc.c

@@ -88,6 +88,7 @@ MakeMapObject(int ColorCount,
 
     Object->Colors = (GifColorType *)calloc(ColorCount, sizeof(GifColorType));
     if (Object->Colors == (GifColorType *) NULL) {
+        free(Object);
         return ((ColorMapObject *) NULL);
     }