crn_defs: fix false positive “out of range subscript” error

[illwieckz]

Fix false positive “out of range subscript” error, fix #79:

• https://github.com/DaemonEngine/crunch/issues/79
• https://github.com/DaemonEngine/crunch/pull/60

This is a false positive, but the unused variants of that templated code are always generated so both compilers and code analyzers may report these unused variants are buggy.

So I prefer to rewrite that code in a different way to avoid the problem being endlessly reported by different tools.