Fix parser bug related to constants

[MalteT]

2a-emulator/emulator-2a-lib/src/compiler.rs

Lines 505 to 512 in 741632e

	impl From<MemAddress> for ByteOrLabel {
	fn from(mem: MemAddress) -> Self {
	match mem {
	MemAddress::Constant(c) => c.into(),
	MemAddress::Register(_reg) => unimplemented!("How to make a const from a register"),
	}
	}
	}

The above is potential cause for a panic and is related to a parser bug. This might need some research.