[quant] Support empty batch input for quantized ops (#38508)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/38508
Test Plan:
python test/test_quantization.py TestQuantizedOps.test_empty_batch
Imported from OSS
Differential Revision: D21581937
fbshipit-source-id: e50580dec0682848a0703f7bdee6e9351ab79814
