boot: bound PE section VirtualSize before zeroing the inner kernel

boot: bound PE section VirtualSize before zeroing the inner kernel

The inner-kernel section loader checks VirtualAddress + SizeOfRawData
against kernel_size_in_memory (for the memcpy), but the memzero right
after it clears up to VirtualAddress + VirtualSize, and VirtualSize is
only constrained to be >= SizeOfRawData.

Reject a VirtualAddress + VirtualSize that overflows or exceeds
kernel_size_in_memory, mirroring the existing SizeOfRawData checks.

Follow-up for cab9c7b5a42effa8a45611fc6b8556138c869b5f