[Ohrrpgce] SVN: teeemcee/12464 gfx_sdl2: fix the window possibly jumping from one display to another wh

[subversion at HamsterRepublic.com]

teeemcee
2021-09-24 06:02:10 -0700 (Fri, 24 Sep 2021)
293
gfx_sdl2: fix the window possibly jumping from one display to another when zoom changed

This could happen if changing the window size caused its center to change to a
different display, before it is recentered on its current display.

Also fixed a (harmless) invalid SDL call with NULL window
---
U   wip/gfx_sdl2.bas