ScreenSaverSettings: Silly indentiation fix
ScreenSaver: check function return values for success
ScreenSaverSettings: check find_directory return value
ScreenSaverRunner: clarify some comments
ScreenSaverRunner: check return value of methods
ScreenSaverRunner: treat load_add_on return value like an image_id

... rather than a status_t, because that's what it is.
ScreenSaverRunner: print errors to stderr instead of stdout.

Also print on a couple of new error cases:
* print and error if fSaver is NULL,
* print and error if unload_add_on failed.
ScreenSaverSettings: Check that name is valid

... before trying to use it in GetModuleState() and SetModuleState()

also, rename the stateMsg variable to stateMessage (already correct in header)
ScreenSaverRunner: Fix segmentation fault loading bad screen saver.

When Settings.ModuleName() returned NULL here we got a segmentation fault
trying to access the pointer.

I ran into this trying to load up a non-screensaver executable in ScreenSaver,
it crashed instead of doing the right thing and refusing to load.

Also, since we go to the trouble of saving this to a variable, we should actually use it.