Fix unbound vars and streamline runtime defs
Fix unbound vars and streamline runtime defs

Fix unbound var errors in Zsh.
Fix Liquidprompt unsetting the DEBUG trap if re-activated even if
runtime features were disabled. Now only disables if one of runtime or
runtime bell were enabled.
Breakout __lp_runtime_after since the implementation is the same for
Bash and Zsh.

jaesivsm/liquidprompt,pkkolos/liquidprompt,laurentbardin/liquidprompt,milouse/liquidprompt,nojhan/liquidprompt