If creating a sound object fails, delete it to ensure that it is recreated
later.
This fixes a minor bug: previously, if an invalid file was used as sound file,
only the first attempt to play it resulted in an error and all the subsequent
ones were just silently ignored. Now every attempt to play an invalid file
results in an error message, as expected.
(this is a backport of a788351eb6 from master)
2eb5cb50bb