Fix ImageSpace relocation direction check.

The correct check whether `begin+diff` would overflow
uint32_t is `begin >= -diff` in unsigned arithmetic.

Note that with the current ranges of relocation diff and
ART_BASE_ADDRESS, the result of the check is the same as
before.

Test: m test-art-host-gtest
Bug: 77856493
Change-Id: Ic0ded458ad8fa327ea74e2e0ebdd4de18c4e5b04