fuse: Reopen file and skip to desired offset if seek is not supported

The fuse daemon can fail when client attempts to seek backwards and seek is not supported by the concrete backend. There is fallback for forward seeks using g_input_stream_skip. Let's reopen the file and use the same approach also for backwards seeks. This is pretty ugly to reopen the file but similar approach is used already to emulate read/write mode.

Fixes: #441 (closed)