[scudo] Do not consider releasing unallocated pages

We already know that there are no free blocks above Region->AllocatedUser.
This results in a smaller RegionPageMap and faster releaseFreeMemoryToOS.

Patch By: fabio-d
Differential Revision: https://reviews.llvm.org/D138794

GitOrigin-RevId: 12e20a446e4df75a6aa147dd322ba6a34545c2bc
1 file changed