Merge branch 'jh/loose-object-dirs-creation-race' into maint

Two processes creating loose objects at the same time could have
failed unnecessarily when the name of their new objects started
with the same byte value, due to a race condition.

* jh/loose-object-dirs-creation-race:
  sha1_file.c:create_tmpfile(): Fix race when creating loose object dirs

sha1_file.c

@@ -2860,7 +2860,9 @@ static int create_tmpfile(char *buffer, size_t bufsiz, const char *filename)
 		/* Make sure the directory exists */
 		memcpy(buffer, filename, dirlen);
 		buffer[dirlen-1] = 0;
-		if (mkdir(buffer, 0777) || adjust_shared_perm(buffer))
+		if (mkdir(buffer, 0777) && errno != EEXIST)
+			return -1;
+		if (adjust_shared_perm(buffer))
 			return -1;
 
 		/* Try again */