Correctly reset the goto table for a state.

Correctly reset the goto table for a state.

We cannot use set_gototab() to reset all the entries for a state,
it will leave existing entries as-is.  Add a new reset_gototab()
function that zeroes the table entries for the specified state.
There is no need to reset the goto table immediately after
resize_state(), it is already initialized via calloc().
Fixes https://github.com/onetrueawk/awk/issues/199