[Ohrrpgce] SVN: teeemcee/11788 Add checking for invalid tileset numbers in gmap() to avoid fatal I/O er

[subversion at HamsterRepublic.com]

teeemcee
2020-04-29 18:27:52 -0700 (Wed, 29 Apr 2020)
326
Add checking for invalid tileset numbers in gmap() to avoid fatal I/O error

Added checks in multiple places. loadrecord/storerecord now showbug instead of a
I/O error (at least, you compile with -exx) on negative record number

EDWEIRD.RPG is an example of a game with corrupt tileset numbers, in some of the
blank later maps
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U   wip/common.rbas
U   wip/loading.rbas
U   wip/lumpfile.bas