Handle the unexpected inputs for pass HardwareLoops

Handle the unexpected inputs for pass HardwareLoops

For a function TryConvertLoop in pass HardwareLoops, wrong input arguments will
lead to crash. There will be 3 cases.
In line 342, compiler want to get something from
HWLoopInfo.CountType, which depends on if argument Bitwidth is given, if not,
will crash.
In Function isHardwareLoopCandidate, it dereference CountType too.
In Function InsertLoopDec, it dereference LoopDecrement.
They all could lead to crash. This patch add condition to this pass, when we meet unexpected inputs then skip
the pass.

Reviewed By: samparker, fhahn

Differential Revision: https://reviews.llvm.org/D146277