Ensure git_index_entry is not NULL before trying to free it

src/index.c

@@ -292,6 +292,9 @@ static void index_entry_reuc_free(git_index_reuc_entry *reuc)
 
 static void index_entry_free(git_index_entry *entry)
 {
+	if (!entry)
+		return;
+
 	memset(&entry->id, 0, sizeof(entry->id));
 	git__free(entry);
 }