RFR: 8259356: MediaPlayer's seek freezes video

[Alexander Matveev]

This is regression (introduced) by JDK-8199527. JDK-8199527 added fix for HLS streams (unfortunately I was not able to find repro case and more details on why it was added) in gstappsink.c line 659-678 to store current caps which can be lost during seek/flush. However, this workaround broke code in gst_app_sink_render_common() line 939 which was restoring caps if they were flushed, since we set last_caps to non NULL value. Since code in gst_app_sink_render_common() did not work to propagate caps to sample our rendering code was dropping frames without caps. Fixed by setting caps on sample in HLS workaround code.

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Commit messages:
 - 8259356: MediaPlayer's seek freezes video

Changes: https://git.openjdk.java.net/jfx/pull/464/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=464&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259356
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/464.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/464/head:pull/464

PR: https://git.openjdk.java.net/jfx/pull/464