[InstCombine] avoid creating an extra instruction in zext fold and possible inf-loop

The structure of this fold is suspect vs. most of instcombine
because it creates instructions and tries to delete them
immediately after.

If we don't have the operand types for the icmps, then we are
not behaving as assumed. And as shown in PR49475, we can inf-loop.

(cherry picked from commit 4224a369)