https://gitlab.synchro.net/main/sbbs/-/commit/2ce9ccfe50ab05c3bacf2e8d
Modified Files:
	src/sbbs3/main.cpp
Log Message:
Reset sbbs_t menu path vars (menu_dir and menu_file) before execing cmd shell

I obvserved an issue with Amessyroom's bbs where his custom (JS) shell is
setting bbs.menu_dir but when switching to another stock shell, his menu
files were still being displayed (with mismatching command keys as a result).

bbs.menu_dir (and implicitly, the set_menu_dir Baja function) apparently have
not been used in this way (much) before.
--- SBBSecho 3.20-Linux