Check return value of fuse_loop

[infeo]

With the method int fuse_loop() a fuse filesystem can be started, such that filesystem events are handled.

It returns an error code, if it fails. But currently, this error code is not used:

jfuse/jfuse-api/src/main/java/org/cryptomator/jfuse/api/Fuse.java

Lines 120 to 124 in 75c2070

	try {
	var fuseMount = this.mount(args);
	executor.submit(() -> fuseLoop(fuseMount)); // TODO keep reference of future and report result
	waitForMountingToComplete(mountPoint);
	mount.compareAndSet(lock, fuseMount);

Hence, our implementation does not notice premature ends of the loops and waits indefinitely in the method waitForMountingToComplete.

We must check, if fuse_loop is aready finished in the code, before we wait or return.