Some extensions are not found

[feliperce]

Some file extensions like .aab, .keystore or .jks are not found by File Picker on Android.
This problem occurs on Android, I tested several extensions in the same code, I also tested the library sample code, .aab, .jks and .keystore extensions are not found.

Desktop works

[feliperce]

The getMimeTypeFromExtension method searches for registered extensions, as there is no such extension in the MimeMap, so it returns empty.

To "solve" the problem, I changed the code to remove the extension filter if none were provided:
#143