[Ohrrpgce] SVN: teeemcee/11786 Show an error message instead of crashing if binsize.bin is missing or i

[subversion at HamsterRepublic.com]

teeemcee
2020-04-28 19:27:00 -0700 (Tue, 28 Apr 2020)
197
Show an error message instead of crashing if binsize.bin is missing or invalid

Caused a divide-by-zero exception. Crashrpt 88bba8a4

Also replace a few fatalbugs (nearly all of them) with showbugs
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U   wip/common.rbas
U   wip/loading.rbas
U   wip/mapsubs.bas