avoid resetting mExpectRetrograde when deltaHalPosition == 0

To avoid frequently accessing HAL, StreamHalAidl returns a cached
position if the last queried position is not expired. The expired time
is at least 100 ms. If the position is the same as the previous one,
then deltaHalPosition is zero, so mExpectRetrograde is accidentially
reset, but mRenderPosition isn't subtracted.

Bug: 328486216
Bug: 332411039
Bug: 331300943
Test: manual test with YTM
Change-Id: I204198b10038101f41b7b417034d05d4430e13be