config_file: move refresh into `write` function

We are quite lazy in how we refresh our config file backend when
updating any of its keys: instead of just updating our in-memory
representation of the keys, we just discard the old set of keys
and then re-read the config file contents from disk. This refresh
currently happens separately at every callsite of `config_write`,
but it is clear that we _always_ want to refresh if we have
written the config file to disk. If we didn't, then we'd run
around with an outdated config file backend that does not
represent what we have on disk.

By moving the refresh into `config_write`, we are also able to
optimize the case where the config file is currently locked.
Before, we would've tried to re-read the file even if we have
only updated its cached contents without touching the on-disk
file. Thus we'd have unnecessarily stat'd the file, even though
we know that it shouldn't have been modified in the meantime due
to its lock.

src/config_file.c

@@ -284,8 +284,6 @@ static int config_set(git_config_backend *cfg, const char *name, const char *val
 	if ((error = config_write(b, name, key, NULL, esc_value)) < 0)
 		goto out;
 
-	error = config_refresh(cfg);
-
 out:
 	git_config_entries_free(entries);
 	git__free(esc_value);
@@ -352,8 +350,6 @@ static int config_set_multivar(
 	if ((result = config_write(b, name, key, &preg, value)) < 0)
 		goto out;
 
-	result = config_refresh(cfg);
-
 out:
 	git__free(key);
 	p_regfree(&preg);
@@ -385,9 +381,6 @@ static int config_delete(git_config_backend *cfg, const char *name)
 	if ((error = config_write(b, name, entry->name, NULL, NULL)) < 0)
 		goto out;
 
-	if ((error =  config_refresh(cfg)) < 0)
-		goto out;
-
 out:
 	git_config_entries_free(entries);
 	git__free(key);
@@ -426,9 +419,6 @@ static int config_delete_multivar(git_config_backend *cfg, const char *name, con
 	if ((result = config_write(b, name, key, &preg, NULL)) < 0)
 		goto out;
 
-	if ((result = config_refresh(cfg)) < 0)
-		goto out;
-
 out:
 	git_config_entries_free(entries);
 	git__free(key);
@@ -1208,7 +1198,12 @@ static int config_write(diskfile_backend *cfg, const char *orig_key, const char
 		git_buf_attach(&cfg->locked_content, git_buf_detach(&buf), len);
 	} else {
 		git_filebuf_write(&file, git_buf_cstr(&buf), git_buf_len(&buf));
-		result = git_filebuf_commit(&file);
+
+		if ((result = git_filebuf_commit(&file)) < 0)
+			goto done;
+
+		if ((result = config_refresh(&cfg->header.parent)) < 0)
+			goto done;
 	}
 
 done: