Make CacheDataSource.open() throw exception if resolved range doesn't cover position

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151006826

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSource.java

@@ -181,6 +181,9 @@ public final class CacheDataSource implements DataSource {
         bytesRemaining = cache.getContentLength(key);
         if (bytesRemaining != C.LENGTH_UNSET) {
           bytesRemaining -= dataSpec.position;
+          if (bytesRemaining <= 0) {
+            throw new DataSourceException(DataSourceException.POSITION_OUT_OF_RANGE);
+          }
         }
       }
       openNextSource(true);