[Ohrrpgce] SVN: teeemcee/7924 Fix wrong scripterr messages for bad menu handles: add valid_menu_handle

[subversion at HamsterRepublic.com]

teeemcee
2016-04-07 03:27:43 -0700 (Thu, 07 Apr 2016)
291
Fix wrong scripterr messages for bad menu handles: add valid_menu_handle

Previously, passing a bad menu handle would always say "invalid menu handle -1",
because valid_menuslot was called on the result of find_menu_handle, which
didn't show an error but returned -1.

(See also next commit)
---
U   wip/scriptcommands.bas
U   wip/scriptcommands.bi