[scudo] Fix the misused Exhausted in region allocation (#89852)

`Region->Exhausted` indicates that we don't have more pages to create
new blocks in the region. It has different meaning from region
allocation failure.

Also fix a minor lint in popBlocks()

GitOrigin-RevId: c7f4b3e1bd5cab43d6f733a5107b2946c76bc0bb
1 file changed