GlobalISel: Always check operand types when executing match table

Summary:
Some of the commands tries to get the register without checking
if the specified operands is a register and causing crash. All commands
should check the type of the operand first and reject if the type is
not expected.

Reviewers: dsanders, qcolombet

Reviewed By: qcolombet

Subscribers: qcolombet, rovka, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D42984

llvm-svn: 324442