Avoid accessing live-words bitmap past its size

When accessing the last page of the moving space, we were accessing the
word past the live-words bitmap, which could cause SIGSEGV.

Bug: 160737021
Test: art/test/testrunner/testrunner.py --target
Change-Id: I7032af6265d7e18207b71f7f2325d69f06917324
2 files changed