DX7 SubPic: Use the same filtering than DX9 SubPic for consistency.
Optimize CSimpleTextSubtitle::CreateSegments.

Make use of the fact the segments are sorted to use a search algorithm in O(log(N)).
Optimize CSimpleTextSubtitle::Add.

Also add comments.
External subtitle: Remove a useless call to CreateSegments.

Segments are created on the fly when inserting the entries.
CTextFile: Fix an out-of-bound access to the cache.

This could cause an infinite loop.
CTextFile: Fix an infinite loop for UTF8 with BOM files with invalid chars.

Also try to be more resilient when such file is encountered: show all characters that could be correctly decoded and replace invalid characters by '?'.
Updated LAV Filters to 0.60-5-57144ef (custom build based on stable version 0.60)

Important changes:
 - LAV Splitter: Improved OGM seeking.
 - LAV Splitter: Minor fixes for the default subtitle selection.