RAII: Change order or variables in clang version

This prevents use-after-scope issues when unwinding the stack,
which happens in reverse order. The varname variable needs to
remain alive for the destruction to be able to access it.
Issue was found using clang + address-sanitizer.

ASTERISK-28232 #close

Change-Id: I00811c34ae910836a5fb6d22304528aef92624db