Check for calloc() failure in filesystem code

src/fs_packed.c

@@ -67,9 +67,10 @@ static void *packed_open(const char *path, int flags) {
   struct packed_file *fp = NULL;
   if (data == NULL) return NULL;
   if (flags & MG_FS_WRITE) return NULL;
-  fp = (struct packed_file *) calloc(1, sizeof(*fp));
-  fp->size = size;
-  fp->data = data;
+  if ((fp = (struct packed_file *) calloc(1, sizeof(*fp))) != NULL) {
+    fp->size = size;
+    fp->data = data;
+  }
   return (void *) fp;
 }