hoa.gain~ with max-api

[eliottparis]

need to fix several issues with hoa.gain~ object when compiled against the new max-api:

• preset disabled (the method binbuf_vinsert does not exists anymore)
• error message when instantiated :

zgetfn (bfixwidth): corrupt object
method bfixwidth called on invalid object

=> see: beafec52f3fd03d19dd3d4f811192c47e562404d