Refine last segment calculation.

This makes the calculation correct for the case where periodDurationMs
does not divide exactly into durationMs.

library/src/main/java/com/google/android/exoplayer/dash/mpd/SegmentBase.java

@@ -301,7 +301,7 @@ public abstract class SegmentBase {
         return DashSegmentIndex.INDEX_UNBOUNDED;
         return DashSegmentIndex.INDEX_UNBOUNDED;
       } else {
       } else {
         long durationMs = (duration * 1000) / timescale;
         long durationMs = (duration * 1000) / timescale;
-        return startNumber + (int) (periodDurationMs / durationMs) - 1;
+        return startNumber + (int) ((periodDurationMs + durationMs - 1) / durationMs) - 1;
       }
       }
     }
     }