Fix retry crash in edge case

Configuration of retry currently fails if all of the
following are true, which is highly unlikely but does
occur in the ref'd issue.

1. Loading/extraction fails
2. Neither length of stream of a seek map is known
3. At least one track has been output by the extractor

Issue: #1899

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135228687

library/src/main/java/com/google/android/exoplayer2/source/ExtractorMediaPeriod.java

@@ -456,7 +456,7 @@ import java.util.Arrays;
       lastSeekPositionUs = 0;
       lastSeekPositionUs = 0;
       notifyReset = prepared;
       notifyReset = prepared;
       for (int i = 0; i < sampleQueues.length; i++) {
       for (int i = 0; i < sampleQueues.length; i++) {
-        sampleQueues[i].reset(trackEnabledStates[i]);
+        sampleQueues[i].reset(!prepared || trackEnabledStates[i]);
       }
       }
       loadable.setLoadPosition(0);
       loadable.setLoadPosition(0);
     }
     }