xcursor: fix NULL deref on malloc() fail

xcursor/xcursor.c

@@ -763,9 +763,11 @@ xcursor_load_theme(const char *theme, int size,
 			continue;
 
 		full = xcursor_build_fullname(dir, "cursors", "");
+		if (full) {
 			load_all_cursors_from_dir(full, size, load_callback,
 						  user_data);
 			free(full);
+		}
 
 		if (!inherits) {
 			full = xcursor_build_fullname(dir, "", "index.theme");