[quant][mobile] Ensure qconv doesn't assert with empty batch (#38252)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38252
Return empty batch output if input has empty batch on mobile.
Test Plan:
python test/test_quantization.py TestQNNPackOps.test_qconv_empty_batch
Imported from OSS
Differential Revision: D21515998
fbshipit-source-id: 1eab4710f4c21d06521e1a172f9bc708dbaeb3c0
