This fixes CORE-19497 'Regression, part of the statusbar with the sizegrip is not redrawn properly'
The regression was introduced / unhidden by 0.4.15-dev-5617-g 7866eb2886
Author of the patch: JIRA-user: I_Kill_Bugs
turned into PR by @Doug-Lyons
Thank you both!
KVM: https://reactos.org/testman/compare.php?ids=94433,94435
VBox: Builder Broken atm unfortunately