don't recycle scanf format string if all conversions are done (bug #45808) * oct-stream.cc, oct-stream.h (scanf_format_elt::special_conversion): New enum value, no_conversion. (scanf_format_list::next): If not cycling through the list, return dummy scanf_format_elt after list has been exhausted. (octave_base_stream::do_scanf): Only cycle through the format list more than once if there are conversions to make and the limit on the number of values to convert has not been reached.

7f19e7f2afa2b1476983003f9cd6df2f5b2a4b08 gnulib-hg