padOsd: Use non-deprecated librsvg API to create handle
On one hand, we were using a path instead of an URI on rsvg_handle_set_base_uri(). This broke at some point in librsvg (presumably for the best, handling paths there sounds non-standard) leaving a blank svg (As the base image wouldn't be accessed).
On the other hand, we use this with the deprecated rsvg_handle_write() which we should drift away from.
Using rsvg_handle_new_from_stream_sync() neatly solves both. We use newer API based on input streams and GFiles, and it internally does the right thing, bringing the pad OSD back to life.
Closes: #1220 (closed)