fixed: reading series info from matroska tags only reads first episode index instead of all

trivial change, ready to merge.

if !Contains(episodeNum) [1] was added to workaround duplicated tags in Matroska files
[1]: https://github.com/MediaPortal/MediaPortal-2/blob/987bf531205cc3c9a17ebccbdce4a6f8cde9a77b/MediaPortal/Source/Extensions/MetadataExtractors/SeriesMetadataExtractor/SeriesMetadataExtractor.cs#L116

before:
![20130225_215926](https://f.cloud.github.com/assets/601866/194355/905b4a82-7fa7-11e2-85a4-9270e270268e.png)
after:
![20130225_220852](https://f.cloud.github.com/assets/601866/194356/92629e70-7fa7-11e2-8a81-7b5d9dd3cb52.png)