Remove unnecessary checking of error_state after is_string validation. * data.cc (#NATIVE_REDUCTION, Fcumsum, Fprod, Fsum): Remove if (error_state) check. * debug.cc (Fdbstep): Remove if (error_state) check. * dlmread.cc (Fdlmread): Remove if (error_state) check. * graphics.cc (Fwaitfor): Remove if (error_state) check. * lu.cc (Flu): Remove if (error_state) check. * utils.cc (Ferrno): Remove if (error_state) check. * variables.cc (is_valid_function): Remove if (error_state) check. * fftw.cc (Ffftw): Remove if (error_state) check.