virtualbox: chunk memory reads by 4K to avoid segfault

[Wenzel]

Solves: thalium/icebox#38
Related: #188

[codecov-commenter]

Codecov Report

Merging #215 (5d635e5) into master (7d483ad) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #215   +/-   ##
=======================================
  Coverage   15.73%   15.73%           
=======================================
  Files          10       10           
  Lines         591      591           
  Branches       94       94           
=======================================
  Hits           93       93           
  Misses        480      480           
  Partials       18       18           

Flag	Coverage Δ
unittests	15.73% <ø> (ø)

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