Wave editor always creates a copy of the edited file

[spamatica]

In the past the wave editor would edit a wave file directly if there was only one instance. If there were more than one it would inform that it would create a copy.
Now for some reason it always makes a copy. Had a quick look and the code has indeed changed but I could not spot the error.
Creating the bug so we don't forget.

[terminator356]

A fix has been applied. Thanks for spotting that.