[Ohrrpgce] SVN: teeemcee/10282 Fix majorly crashy and corrupting spriteset import code

[subversion at HamsterRepublic.com]

teeemcee
2018-03-31 22:32:40 -0700 (Sat, 31 Mar 2018)
243
Fix majorly crashy and corrupting spriteset import code

I probably implemented per-frame spriteset import first and then broke it
when implementing whole spriteset import, without testing.
And cancelling an import would corrupt the spriteset.
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U   wip/drawing.bas