Processor execution of current pcode instruction should return `Option` due to noop instructions

[mnemonikr]

symbolic-pcode/crates/pcode/src/processor.rs

Lines 308 to 310 in d968cf7

	pub fn current_instruction(&self) -> &PcodeInstruction {
	&self.pcode.instructions[self.index]
	}

This can fail for noop instructions. Should make this return an Option so it's more clear that this edge case needs to be handled by the caller.