Decoder: Ignore dangling fields during flush

If decoder has decoded one field and is waiting for next field,
and flush is called, then ignore the current decoded field.

This is needed to ensure seek works in case of flush between field
decode calls

Bug: 32391809
Test: Tested manually by decoding clip in the above bug in Photos app

Change-Id: I72bb0385c216ebe262b346a56d3bc8fb97f90a7b
1 file changed