Adjust exception error messages to show correct address.
Exception error messages have been unhelpfully showing an address beyond the instruction that caused the error, which is somewhat confusing.
- Add offset parameter to DumpyTheRegisters in R4
- Shuffle internal register use up one
- Set R4 to offset before calling.
- Arbitrary offset of 0 for unreachable address exception handler.
Tested in RPCEmu. Test case attached.