Fix ReservoirSampling zero-initialization reliance (#16702)
Summary:
The op was implicitly relying on pos_to_output to be zero-initialized after extending. We're removing this functionality from allocator, thus fixing here. For some reason it wasn't spotted by junk-initialization but was reliably reproducible with standard malloc() if both junk_fill and zero_fill flags are turned off.
cc kittipatv jerryzh168
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16702
Reviewed By: kittipatv
Differential Revision: D13937257
Pulled By: dzhulgakov
fbshipit-source-id: 3ee520b05467108e6c3e64eb3e6c60589bdf3d87
