nir/loop_analyze: Don't test non-positive iterations count
What does this MR do and why?
nir/loop_analyze: Don't test non-positive iterations count
Testing negative iterations count makes no sense, and can cause issues when the unsigned type is used. Testing 0 iterations is already covered with will_break_on_first_iteration, so it can be skipped too.
Fixes: 6772a17a ("nir: Add a loop analysis pass") Closes: #9913 (closed)