Fix crash in SDLVGA on macOS Big Sur 11.2

[kulp]

On macOS Big Sur 11.2, a crash in sdlvga (but not sdlled) was noticed when running SDL with a non-dummy display. The underlying cause is not fully understood, but the new call order is consistent with the pre-existing call order in handle_update.

[codecov]

Codecov Report

Merging #83 (c7a97f9) into develop (763ca54) will not change coverage.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##           develop     #83   +/-   ##
=======================================
  Coverage     96.6%   96.6%           
=======================================
  Files           35      35           
  Lines         2652    2652           
  Branches       468     468           
=======================================
  Hits          2563    2563           
  Misses          70      70           
  Partials        19      19           

Impacted Files	Coverage Δ
src/devices/sdlvga.c	90.1% <100.0%> (ø)

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