BiasedDelay: crasher bugfix, and misc improvements

Fixed the key bug: in the released version a variable remained uninitialised which caused a crash when loading. 

Additionally it seems the destructor caused problems/crashes too -- it simply deleted an allocated buffer. Looking at other official plugins I noticed that nobody ever actually deallocates their audio buffers, so I removed this code too.

Then took this as an opportunity for a review, made a generally improved version.