Compilation error in data.cc: octave_extract_value<char> mus return a value

[Michael Goffioul]

Hi,

As the title mentions, I get a compilation error in data.cc, because the default
implementation of octave_extract_value<T> does not return any value. While
specialization is provided for relevant types, default implementation
is used for
type char and octave_value.

The error occurs in data.cc where octave_extract_value<T> can be instantiated
for char and octave_value, in single_type_concat function. While the actual
code never executed, because of the if-statement:

  if (! (equal_types<T, char>::value
         || equal_types<T, octave_value>::value)
      && all_scalar_1x1 (args))

it seems that MSVC still instantiates the code and fails to compile it (maybe
this does not happen when turning on optimization, but I compile with debug
enabled, without any optimization).

Obvious solution is to provide dummy specialization of octave_extract_value
for char and octave_value.

Michael.