[InstCombine] Don't combine PHI before catchswitch

This tries to bail out if the PHI is in a `catchswitch` BB in
InstCombine. A PHI cannot be combined into a non-PHI instruction if it
is in a `catchswitch` BB, because `catchswitch` BB cannot have any
non-PHI instruction other than `catchswitch` itself.

The given test case started crashing after D98058.

Reviewed By: lebedev.ri, rnk

Differential Revision: https://reviews.llvm.org/D105309