Correctly offset subsample timestamps.

This has always been broken in V2, but the issue is now also
visible for the very first period in the timeline because we
offset if by 60s. Previously the issue would only have been
visible from the start of the second period.

Issue: #2208

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=142252702

library/src/main/java/com/google/android/exoplayer2/BaseRenderer.java

@@ -267,6 +267,12 @@ public abstract class BaseRenderer implements Renderer, RendererCapabilities {
         return streamIsFinal ? C.RESULT_BUFFER_READ : C.RESULT_NOTHING_READ;
       }
       buffer.timeUs += streamOffsetUs;
+    } else if (result == C.RESULT_FORMAT_READ) {
+      Format format = formatHolder.format;
+      if (format.subsampleOffsetUs != Format.OFFSET_SAMPLE_RELATIVE) {
+        format = format.copyWithSubsampleOffsetUs(format.subsampleOffsetUs + streamOffsetUs);
+        formatHolder.format = format;
+      }
     }
     return result;
   }