Better validation and handling of GCZ

DiscIO: Use views::keys

A malicious GCZ file could probably force this to be negative.
Shouldn't cause any issues other than file read failures, but need to fix
because it is causing errors on MSVC.

SectorReader::ReadChunk does do some validation on it, but it only
checks against the original disc size (reported by the GCZ file).
It has no idea how many blocks the header claimed the disc had.

A maliciously crafted GCZ file could trigger read overflows off the end
of the m_block_pointers/m_hashes arrays.

It comes unverified from the file, and a maliciously crafted file could
trigger not one, but two buffer overflows in the heap.

IOS/ES: Prevent reading TMDs that are too small

DiscIO: Add DTK alignment comment in DirectoryBlob