glocalfileinfo: Fix a leak on an error handling path

Spotted by Clang static analysis, thanks to Leslie Zhai.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://bugzilla.gnome.org/show_bug.cgi?id=777075

gio/glocalfileinfo.c

@@ -657,7 +657,10 @@ get_xattrs_from_fd (int                    fd,
 	}
 
       if (list_res_size == -1)
-	return;
+        {
+          g_free (list);
+          return;
+        }
 
       attr = list;
       while (list_res_size > 0)