[Ohrrpgce] SVN: teeemcee/12448 Remove NULL_CHANNEL from FB code; fix its type in the C declaration

[subversion at HamsterRepublic.com]

teeemcee
2021-09-16 19:04:53 -0700 (Thu, 16 Sep 2021)
133
Remove NULL_CHANNEL from FB code; fix its type in the C declaration

The fixed type revealed an inconsequential typo in filelayer.cpp
---
U   wip/audioedit.bas
U   wip/custom.bas
U   wip/customsubs.rbas
U   wip/drawing.bas
U   wip/filelayer.cpp
U   wip/game.bas
U   wip/heroedit.rbas
U   wip/loading.rbas
U   wip/lumpfile.bas
U   wip/mapsubs.bas
U   wip/os.bi
U   wip/os.h
U   wip/yetmore2.bas