Store marks only on success

Commit 2594a79 (remote-hg: fix bad state issue) originally introduced
this code in order to avoid synchronization issues while pushing,
because `git fast-export` might end up writing the marks before a crash
in the remote helper occurs.

However, the problem is in `git fast-export`; the marks should only be
written after both have finished successfully.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

git-remote-hg

@@ -1255,12 +1255,10 @@ def main(args):
             die('unhandled command: %s' % line)
         sys.stdout.flush()
 
+    marks.store()
+
 def bye():
-    if not marks:
-        return
-    if not is_tmp:
-        marks.store()
-    else:
+    if is_tmp:
         shutil.rmtree(dirname)
 
 atexit.register(bye)