Fix segfault when complex double matrix calls ZGETRF (bug #45577). * CMatrix.cc (finverse, determinant, rcond, fsolve): Calculate norm of matrix and if it is NaN, skip calling ZGETRF in LAPACK and set info to non-zero value to signal an error.

%!function r = f (x)
%!  if (ischar (x))
%!    r = x;
%!  else
%!    error ("expecting character string");
%!  endif
%!endfunction

%!assert (eval ("f 10;"), "10");