config: let `config_store_data_clear()` handle `key`

Instead of remembering to free `key` in each code path, let
`config_store_data_clear()` handle that.

We still need to free it before replacing it, though. Move that freeing
closer to the replacing to be safe. Note that in that same part of the
code, we can no longer set `key` to the original pointer, but need to
`xstrdup()` it.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -2335,6 +2335,7 @@ struct config_store_data {
 
 static void config_store_data_clear(struct config_store_data *store)
 {
+	free(store->key);
 	if (store->value_regex != NULL &&
 	    store->value_regex != CONFIG_REGEX_NONE) {
 		regfree(store->value_regex);
@@ -2679,7 +2680,6 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 	fd = hold_lock_file_for_update(&lock, config_filename, 0);
 	if (fd < 0) {
 		error_errno("could not lock config file %s", config_filename);
-		free(store.key);
 		ret = CONFIG_NO_LOCK;
 		goto out_free;
 	}
@@ -2689,8 +2689,6 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 	 */
 	in_fd = open(config_filename, O_RDONLY);
 	if ( in_fd < 0 ) {
-		free(store.key);
-
 		if ( ENOENT != errno ) {
 			error_errno("opening %s", config_filename);
 			ret = CONFIG_INVALID_FILE; /* same as "invalid config file" */
@@ -2702,7 +2700,8 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 			goto out_free;
 		}
 
-		store.key = (char *)key;
+		free(store.key);
+		store.key = xstrdup(key);
 		if (write_section(fd, key, &store) < 0 ||
 		    write_pair(fd, key, value, &store) < 0)
 			goto write_err_out;
@@ -2752,13 +2751,10 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 						      config_filename,
 						      &store, &opts)) {
 			error("invalid config file %s", config_filename);
-			free(store.key);
 			ret = CONFIG_INVALID_FILE;
 			goto out_free;
 		}
 
-		free(store.key);
-
 		/* if nothing to unset, or too many matches, error out */
 		if ((store.seen_nr == 0 && value == NULL) ||
 		    (store.seen_nr > 1 && multi_replace == 0)) {