clarify where error message is set

src/status.c

@@ -238,7 +238,7 @@ static int get_one_status(const char *path, unsigned int status, void *data)
 		 p_fnmatch(sfi->expected, path, sfi->fnm_flags) != 0))
 	{
 		sfi->ambiguous = true;
-		return GIT_EAMBIGUOUS;
+		return GIT_EAMBIGUOUS; /* giterr_set will be done by caller */
 	}
 
 	return 0;