Misc fixes in Osmo4 UI, and set number of decoded frames for OpenHEVC to 3

git-svn-id: https://gpac.svn.sourceforge.net/svnroot/gpac/trunk/gpac@4437 63c20433-aa62-49bd-875c-5a186b69a8fb
Merge branch 'plain'
Fix a bug that the extension of output file is missing

Conditions of bug is that there are periods in the file name.

Regression in svn r4097.
Git HASH: 47a4bf40f6f921d339c694d3033d22665b590b21
Fix the mistake of judging the media type

This is a mistake in the following commit.
Git HASH: 664297bfedeae40791d6625b30d9f77046bc3c5f