refdb: catch a directory disappearing

If a directory disappears between the time we look up the entries of its
parent and the time when we go to look at it, we should ignore the error
and move forward.

This fixes #2046.

src/path.c

@@ -853,6 +853,9 @@ int git_path_direach(
 
 	if ((dir = opendir(path->ptr)) == NULL) {
 		giterr_set(GITERR_OS, "Failed to open directory '%s'", path->ptr);
+		if (errno == ENOENT)
+			return GIT_ENOTFOUND;
+
 		return -1;
 	}
 

src/refdb_fs.c

@@ -272,9 +272,17 @@ static int _dirent_loose_load(void *payload, git_buf *full_path)
 	if (git__suffixcmp(full_path->ptr, ".lock") == 0)
 		return 0;
 
-	if (git_path_isdir(full_path->ptr))
-		return git_path_direach(
+	if (git_path_isdir(full_path->ptr)) {
+		int error = git_path_direach(
 			full_path, backend->direach_flags, _dirent_loose_load, backend);
+		/* Race with the filesystem, ignore it */
+		if (error == GIT_ENOTFOUND) {
+			giterr_clear();
+			return 0;
+		}
+
+		return error;
+	}
 
 	file_path = full_path->ptr + strlen(backend->path);