[clang][sema] Fix collectConjunctionTerms()

Consider:

A == 5 && A != 5

IfA is 5, the old collectConjunctionTerms() would call itself again for
the LHS (which it ignores), then the RHS (which it also ignores) and
then just return without ever adding anything to the Terms array.

Differential Revision: https://reviews.llvm.org/D131070