fix(mutt): fix use of regex in the glob context

The construct "${cur/^!/$spoolfile}" appears to try to replace the
beginning `!` with "$spoolfile" because cur starts with `!` in this
context.  However, this does not work because ^ does not mean the
beginning of the string.  We may instead use "${cur/#!/$spoolfile}".

completions/mutt

@@ -136,7 +136,7 @@ _comp_cmd_mutt__filedir()
     elif [[ $cur == !* ]]; then
         spoolfile="$("$muttcmd" -F "$muttrc" -Q spoolfile 2>/dev/null |
             command sed -e 's|^spoolfile=\"\(.*\)\"$|\1|')"
-        [[ $spoolfile ]] && eval cur="${cur/^!/$spoolfile}"
+        [[ $spoolfile ]] && eval cur="${cur/#!/$spoolfile}"
     fi
     _comp_compgen -c "$cur" filedir
 }