Fix font loading when attachments precede tracks in MKV

[edde746]

Fixes #19. Font attachments embedded in MKV files were not loaded when the Attachments EBML element appeared before the Tracks element in the file. The Matroska specification does not enforce a fixed order for top-level elements, so parsers must handle either arrangement.

The extractor previously guarded font loading with hasTracks(), which returned false if no subtitle track had been discovered yet. Since ExtractorInput is a streaming interface, skipped font data cannot be re-read — the fonts were permanently lost.

Changes

Fonts encountered before any ASS track are now buffered in AssHandler and flushed to libass when the first track is created. Lazy initialization of the native library is preserved — if no ASS tracks exist, libass is never loaded.

• AssHandler.kt - added pendingFonts buffer, addFont() method, flush in createTrack()
• AssMatroskaExtractor.kt - removed hasTracks() guard, delegates to assHandler.addFont()

Before / After

Before	After

Ignore overlay on the 2nd image, font difference is especially noticeable on the episode title.

Nyaa ID for example is 1856654.

This PR was developed with AI assistance (Claude Code).