Block signals during mbox-append operation.

I first noticed this back in 2017, but no one replied to my query to
mutt-dev and I forgot about it too.

Thanks to Oswald Buddenhagen for the followup when he was going
through the mailing list archives, confirming the mistake.

I've also reviewed MUTT_APPEND and MUTT_NEWFOLDER uses to make sure
the context is properly closed (and the signals restored).

1 files changed, 2 insertions, 0 deletions

diff --git a/mbox.c b/mbox.c
index 10361184..6b3c381a 100644
--- a/mbox.c
+++ b/mbox.c
@@ -479,9 +479,11 @@ static int mbox_open_mailbox_append (CONTEXT *ctx, int flags)
     return -1;
   }
 
+  mutt_block_signals ();
   if (mbox_lock_mailbox (ctx, 1, 1) != 0)
   {
     mutt_error (_("Couldn't lock %s\n"), ctx->path);
+    mutt_unblock_signals ();
     safe_fclose (&ctx->fp);
     return -1;
   }