AV1 and HEVC SW codecs min input buffer size

AV1 and HEVC plugins were not imposing a minimum input buffer size,
leading to some test failures where the calculated size was smaller than
some NALs from the extractor.

Bug: 215297028
Test: mts -m CtsMediaTestCases -t android.media.cts.AdaptivePlaybackTest#testAV1_adaptiveSmallDrc
Test: mts -m CtsMediaTestCases -t android.media.cts.AdaptivePlaybackTest#testHEVC_adaptiveSmallDrc
Change-Id: I7f5c8746f085b5f88b1a61f0a37d4d00f3e3e777