String index out of range when doing a complex inverse FFT #269

When doing an inverse complex FFT on a stack with a short name, the following error appears: java.lang.StringIndexOutOfBoundsException: String index out of range: -9. This has to do with line 553 in FFT.java: String name = WindowManager.getUniqueName(imp.getTitle().substring(10)).

Steps to reproduce:

• Open an image
• Do a complex FFT
• Rename the stack to something with <10 characters
• Do an inverse FFT

Workaround: rename the stack to something with >10 characters