Fix completely broken dialog-building functions.

Fix completely broken dialog-building functions.

The loops that were supposed to count up the number of buttons in the
variadic argument list forgot to increment the counter.

On the other hand, these functions aren't actually _used_ anywhere in
the current code - looks as if commit 616c837cf was the last time they
were seen - but manual dialog stuff like PuTTYgen might yet find a use
for them in future.