Mailsync: only pass -a to mbsync when no args

If -a is passed along with "$@", mailsync will sync all mailboxes even
if only a single channel is passed in with "$@". This breaks the
semantics of the `o` macro in mutt which should only sync the current
mailbox that is currently being viewed in mutt.

bin/mailsync

@@ -18,7 +18,12 @@ echo " 🔃" > /tmp/imapsyncicon_$USER
 pkill -RTMIN+12 i3blocks
 
 # Run mbsync. You can feed this script different settings.
-mbsync -a "$@"
+if [ $# -eq 0 ]; then
+	mbsync -a
+else
+	mbsync "$@"
+fi
+
 rm -f /tmp/imapsyncicon_$USER
 pkill -RTMIN+12 i3blocks