Fix scanf handling of exceptional values (NA, NaN, Inf) at EOF (bug #63383) * oct-stream.cc (octave_scan): After skipping whitespace, check stream with is.good() before proceeding to read a value. * lo-utils.cc (read_inf_nan_na): Use is.peek() after successfully reading Inf or NaN to possibly set EOF bit. * lo-utils.cc (read_fp_value): Add extra test that value is not NA or NaN before changing it to -value when negative '-' character present. * io.tst: Mark fixed BIST tests with '*' regression marker. Add BIST tests for exceptional '+' character and for +/-NA, +/-NaN.

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