Fix for external SDCard on Android M

[jahertor]

Starting from Android M, the external SD Card used as portable storage shows the SDCard ID as DocumentsContract first parameter.

So docId has the following format: XXXX-XXXX:path/to/the/file
And the real path would be: /storage/XXXX-XXXX/path/to/the/file

if (type.matches("[A-F0-9]{4}-[A-F0-9]{4}")) {
     return "/storage/".concat(type).concat("/").concat(split[1]);
}

Tested on Moto X Play 6.0. Someone can confirm that it's the same for other devices? I don't like at all handwrite the "storage" path, and maybe the type is not always an SDCard ID.

We should discuss this before merge.

[jahertor]

I just see #78 that fix the problem. It loops the mounted volumes using reflection of android.os.storage.StorageVolume and return the path for the first occurence.