[InstCombine] Fix two asserts that were accidentally checking that an APInt...

[InstCombine] Fix two asserts that were accidentally checking that an APInt pointer is non-zero instead of checking that the APInt self is non-zero.

I believe this code used to use APInt references which would have worked. But then they were changed to pointers to allow m_APInt to be used.

llvm-svn: 304875