remote submix: add null check on audio pipe pointer

In remote submix audio HAL, Add null check on Pipe sink pointer
in out_get_presentation_position() and out_get_render_position().

Bug: 117183072
Test: manual test with capture from BLE remote mic.
Change-Id: I05aa87f414c69bcd08c7692918e6a215077b7ea2
1 file changed