Fire Emblem (J) crashes after initial sequence

[DaveTCode]

One of only two mapper 10 games, no tests for mapper 10 so very plausible I've just made it up badly.

thread 'main' panicked at 'Invalid address for PPU write 4372=A8', src\ppu\mod.rs:430:18
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `target\release\rust_nes.exe ".\roms\real\Fire Emblem - Ankoku Ryuu to Hikari no Tsurugi (Japan).zip"` (exit code: 101)

Interesting that it generates an invalid PPU address write though, I would have said I didn't think that was possible so it's possibly a more significant bug

[DaveTCode]

#60 changes this to some extent, it now fails on a KIL opcode, which strongly suggests a mapper bug