Avoid 32-bit overflows on offset+size calculations

move to 64 bit math for several offset+size checks to avoid 32-bit overflows.
Exposed by enabling integer overflow detection 10 months ago; we finally
ran into a file that tripped the condition.

Bug: 112241654
Bug: 112537774
Test: manual
Change-Id: I027e87d9cd28e29ba21385543aaa3f1bc6f44b5b