storage lands near the end of the available address space. In the expression
Begin+N > Capacity, the Begin+N was overflowing. Fix this by replacing it
by with an expression that doesn't involve computation of an address
beyond the end of allocated memory.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37171 91177308-0d34-0410-b5e6-96231b3b80d8