Codefix: cast to "CommandCallback *" in a way cast-function-type-mismatch doesn't mind

[TrueBrain]

Motivation / Problem

Newest clang complaints about our casting to CommandCallback *.

Description

Fix the warning in the same way that was already done in MakeCallbackTable (https://github.com/OpenTTD/OpenTTD/tree/master/src/network/network_command.cpp#L109), by first casting it to void (*) (void). This is explicit for this warning: The function type void (*) (void) is special and matches everything, which can be used to suppress this warning.

I took no further consideration whether there are better solutions, as clearly someone already looked into this before. And the warning is correct, but we also correct handle it.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker