maint: Replace if/error/else paradigm with just if/error. * __ilu__.cc, data.cc, file-io.cc, graphics.cc, graphics.in.h, ls-mat5.cc, lu.cc, octave-link.cc, regexp.cc, schur.cc, spparms.cc, sub2ind.cc, syscalls.cc, toplev.cc, variables.cc, xpow.cc, audiodevinfo.cc, ccolamd.cc, ov-builtin.cc, ov-classdef.cc, ov-intx.h, ov-lazy-idx.cc, ov-mex-fcn.cc, op-int.h, lex.ll, oct-parse.in.yy, pt-binop.cc, pt-cbinop.cc, pt-const.cc, pt-decl.h, pt-fcn-handle.cc, pt-unop.cc, CollocWt.cc: Replace if/error/else paradigm with just if/error.

gnulib-hg = gnulib-hg