diagram word printing: Account for word index == N_words_to_print
diagram word printing: Account for word index == N_words_to_print

clang static analyzer:
Logic error	Result of operation is garbage or undefined	print.c	linkage_print_diagram_ctxt	746	42

This fix considers the case in which the while() condition (line 741)
is false, which means i == N_words_to_print.

In that case word_offset[i] is garbage, and a non-existing PS row is set to start
with a non-existing word number N_words_to_print.

opencog/link-grammar,opencog/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,opencog/link-grammar,ampli/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,linas/link-grammar,ampli/link-grammar