Fix isnan usage in RTC

[ptrendx]

Description

Fixes problem reported in #18622, where the non-templated version of isnan was used inside min and max functions, causing failures for integer types.

[mxnet-bot]

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[marcoabreu]

Could you add a test

[sxjscience]

For me, I think it might be difficult to add test cases and it should good to merge for now (since we are in the dev mode). We can always add test cases later to cover these cases. Thus, I will approve it but feel free to express your concerns @marcoabreu .

[marcoabreu]

I mean we discovered a clear case where it fails, so why not add a test?

[sxjscience]

Currently it's triggered if we train the ELECTRA-small model in GluonNLP: https://github.com/dmlc/gluon-nlp/tree/master/scripts/pretraining, which is somehow complicated.

[marcoabreu]

Maybe @ptrendx can extract the relevant part and create a unit test out of it?

[ptrendx]

Yes, I can and will add a test (sorry for not answering it earlier).

[ptrendx]

I added testing of integer datatype to maximum and minimum functions - currently test_np_binary_funcs by default only checks floating point types.

[marcoabreu]

Thanks!

[ptrendx]

@mxnet-bot run ci [centos-gpu, windows-cpu]

[mxnet-bot]

Jenkins CI successfully triggered : [windows-cpu, centos-gpu]

[ptrendx]

@marcoabreu Do you think this PR is good to go?