[Ohrrpgce] SVN: teeemcee/11045 Fix crash when trying to switch to gfx_sdl for a var-res game when compi

[subversion at HamsterRepublic.com]

teeemcee
2019-03-20 22:05:25 -0700 (Wed, 20 Mar 2019)
178
Fix crash when trying to switch to gfx_sdl for a var-res game when compiled against gfx_sdl2

Well actually this is just a workaround, still need to stop switch_gfx from
crashing
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U   wip/backends.bas
U   wip/backends.bi
U   wip/yetmore2.bas