[subtitle] subtitle_cb is called after EOS.

[subtitle] subtitle_cb is called after EOS.

[Model] Tizen3.0 Z2
[BinType] AP
[Customer] OPEN

[Issue#] N/A
[Request] Monitoring test
[Occurrence Version] Z200FDDE0APK7

[Problem] Despite the video is played until EOS, subtitle can be updated.
[Cause & Measure] Cause : Although, the drop-probability property of identity plugin is changed as "0.0",
in this case, the last buffer of fakesink is remained.
So, subtitle_cb will be called after EOS just once.
Measure : the update of subtitle is prohibited after EOS.
[Checking Method] player_test > play video files with subtitle.

[Team] MMFW
[Developer] Jaechan Lee
[Solution company] Samsung
[Change Type] N/A

Change-Id: Ia0c804ccd7ce6d37b995a5687830ad83a8806c3a