C2BqBuffer: Do not cancel buffer after IGBP is no longer used

Since C2BqBuffer holds IGBP, cancelBuffer() can be called regardless of
IGBP's life-cycle. Do not cancel buffer after IGBP is no longer used
from the BlockPool.

Bug: 227121136
Change-Id: I8092808513365db3c85e250c360469e77d71cabc
2 files changed