Blender Git Loki

Performance: Limit recounting during selection mode flushing.

This patch ensures that selection mode flushing updates total selection
counts internally. This reduces recounting when we are sure that the
input total selection counts were up to date.

For example for circle selection the total selection counts were
correct. But during flushing the selection could have been changed and
therefore the selection was always recounted.

This increased the performance on selected system from 6.90 FPS to 8.25
FPS during circle selection operations.

Before: {F10179981}
After: {F10179982}

Reviewed By: mano-wii

Differential Revision: https://developer.blender.org/D11647