Protect against null dereferences

[akshaykhadse]

Fixed clang-format issues

[XinWang10]

llvm/lib/CodeGen/CodeGenPrepare.cpp

7071

This may be useless, we don't init TrueBranch only when TrueInstrs.size()==0.

7074

Ditto.

llvm/lib/TableGen/TGParser.cpp

585

I see ArgumentInit just have 2 kinds, so ArgName could always be inited.

llvm/lib/Target/X86/X86ISelLowering.cpp

5967

I find this is mostly called by combine*, I think the type could be legal here, so will not be 0 here? Otherwise we could crash.