don't leak box list from the command line

we also free the box list obtained from IMAP, so there isn't a real
reason not to do that for one from the command line.

amends 1de3ecd88.

src/main.c

@@ -959,7 +959,7 @@ sync_chans( main_vars_t *mvars, int ent )
 			mvars->skip = 1;
 			return;
 		}
-		if (mvars->chanptr->boxlist == 2) {
+		if (mvars->chanptr->boxlist) {
 			for (nmbox = mvars->chanptr->boxes; (mbox = nmbox); ) {
 				nmbox = mbox->next;
 				free( mbox->name );