[gforth] accept problem in development version 0.7.9_20171005

[Xavier]

'accept' takes n - 1 keys. Ex.: 'pad 4 accept' will let you enter a
maximum of 3 characters.

Problem is also present in version 0.7.9_20170928.

Problem wasn't there in version  0.7.9_20170705. I didn't test
version 0.7.9_20170914.

Thanks, Xavier