avoid printing debug location in cmd window when using GUI to step * pt-eval.cc, pt-eval.h (tree_evaluator::quiet_breakpoint_flag): New member variable. * debug.cc (Fdb_next_breakpoint_quiet): New function. * main-window.cc (main_window::execute_debug_callback): Call Fdb_next_breakpoint_quiet prior to Fdbstep and Fdbcont. * input.cc, input.h (get_debug_input): Don't print debug location if tree_evaluator::quiet_breakpoint_flag is true. Reset it after checking. * lex.ll (octave_lexer::fill_flex_buffer, octave_push_lexer::fill_flex_buffer): Don't abort if input_buf is empty.