Silence imap progress messages for pipe-message. (see #3929)

Silence imap progress messages for pipe-message. (see #3929)

_mutt_pipe_message() calls endwin(), and then calls pipe_msg().  If an
imap message body hasn't already been downloaded, this can end up
calling imap_fetch_message().

The progress messages in imap_fetch_message() were restoring curses,
just after extract_url was running.  This was leading to a condition
where mutt curses didn't think the screen had changed after
extract_url exited.

There was already a check for isendwin() inside imap_fetch_message(),
but it wasn't wrapped around the progressbar creation/usage.  Add a
check for those places too.