decoder/Bridge: install an InputStreamHandler on local files

Before the advent of io_uring (commit dae8da7066), this didn't
matter, because the `FileInputStream` never called this.  But
`UringInputStream` is derived from `AsyncInputStream`, and needs the
handler to signal completion.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/898

src/decoder/Bridge.cxx

@@ -66,7 +66,9 @@ DecoderBridge::OpenLocal(Path path_fs, const char *uri_utf8)
 		}
 	}
 
-	return OpenLocalInputStream(path_fs, dc.mutex);
+	auto is = OpenLocalInputStream(path_fs, dc.mutex);
+	is->SetHandler(&dc);
+	return is;
 }
 
 bool