Fix spurious "missing return" error in irange.h (#102785)
Summary:
Fixes:
```
warning: missing return statement at end of non-void function
```
This warning is cluttering a lot of compilation logs!
Test Plan: Sandcastle
Differential Revision: D46374554
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102785
Approved by: https://github.com/Skylion007
