Minor fixes for period clipping

- Always clip to period duration for the last chunk. We previously
  did this only when the last chunk explicitly exceeded the period
  end time. We now also do it when the chunk claims to end at the
  period boundary, but still contains samples that exceed it.
- If pendingResetPositionUs == chunk.startTimeUs == 0 but the
  chunk still contains samples with negative timestamps, we now
  clip them by setting the decode only flag. Previously we only
  clipped such samples if the first chunk explicitly preceeded the
  start of the period.

Issue: #4899

-------------
Created by MOE: https:/google/moe
MOE_MIGRATED_REVID=215763467

library/core/src/main/java/com/google/android/exoplayer2/source/chunk/ChunkSampleStream.java

@@ -308,7 +308,7 @@ public void seekToUs(long positionUs) {
  // chunk even if the sample timestamps are slightly offset from the chunk start times.
  seekInsideBuffer =
  primarySampleQueue.setReadPosition(seekToMediaChunk.getFirstSampleIndex(0));
- decodeOnlyUntilPositionUs = Long.MIN_VALUE;
+ decodeOnlyUntilPositionUs = 0;
  } else {
  seekInsideBuffer =
  primarySampleQueue.advanceTo(
@@ -583,7 +583,7 @@ public boolean continueLoading(long positionUs) {
  if (pendingReset) {
  boolean resetToMediaChunk = mediaChunk.startTimeUs == pendingResetPositionUs;
  // Only enable setting of the decode only flag if we're not resetting to a chunk boundary.
- decodeOnlyUntilPositionUs = resetToMediaChunk ? Long.MIN_VALUE : pendingResetPositionUs;
+ decodeOnlyUntilPositionUs = resetToMediaChunk ? 0 : pendingResetPositionUs;
  pendingResetPositionUs = C.TIME_UNSET;
  }
  mediaChunk.init(mediaChunkOutput);

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DefaultDashChunkSource.java

@@ -544,7 +544,7 @@ protected Chunk newMediaChunk(
  long endTimeUs = representationHolder.getSegmentEndTimeUs(firstSegmentNum + segmentCount - 1);
  long periodDurationUs = representationHolder.periodDurationUs;
  long clippedEndTimeUs =
- periodDurationUs != C.TIME_UNSET && periodDurationUs < endTimeUs
+ periodDurationUs != C.TIME_UNSET && periodDurationUs <= endTimeUs
  ? periodDurationUs
  : C.TIME_UNSET;
  DataSpec dataSpec = new DataSpec(segmentUri.resolveUri(baseUrl),