Commented Unassigned: "load OTP-help file" button for challange-response opens the "file open" dialog instead of YubiChallange [406]

### Description

"load OTP-help file" button for challange-response opens the "file open" dialog instead of YubiChallange. I download some apks from the website here. The error appears since version 0.9.8-pre2 (online version of keepass2android). Version 0.9.7-pre1 and before works. The YubiChallange app is always installed (version 1.0).

### Observed behaviour
the open file dialog (the same as when you select database file) appear if you press the "load OTP-help file" button

### Expected behaviour
YubiChallange app waiting for the yubikey should appear if you press the "load OTP-help file" button

### Reproduce

1. open any file
2. choose the master password type "Password + Challange-Response"
3. Press the button "load OTP-help file"
4. the open file dialog (the same as when you select database file) appear instead of the YubiChallange app waiting for the yubikey

### Environment

* Samsung Galaxy Note Edge
* Android 5.1.1
* YubiChallange version 1.0.
* keepass2android 0.9.8-pre2 (online version of keepass2android) and 0.9.7-pre1 (various other tested)
Comments: I saw the same behavior some time ago after trying to open a new database on a different path. After this the YubiChallenge app was not but the open file dialog. I could only fix it by reloading a Titanium Backup.