Edge case: Handle media that has no file extension

[RickCarlino]

Problem

• Desktop Anki does not require a file extension for audio media
• AnkiTab does require a file extension (and raises a runtime exception when the media does not have it)

Solution

• Allow media that does not have a file extension, mirroring behaviour in desktop version of Anki.

[corollari]

Thanks!

[corollari]

Just published a new version with your changes, should be available in a few hours :rocket: