code: func opcodeEndif(op *parsedOpcode, vm *Engine) error {
  	if len(vm.condStack) == 0 {
  		str := fmt.Sprintf("encountered opcode %s with no matching "+
  			"opcode to begin conditional execution", op.opcode.name)
  		return scriptError(ErrUnbalancedConditional, str)
  	}
  
  	vm.condStack = vm.condStack[:len(vm.condStack)-1]
  	return nil
  }
docs: // opcodeEndif terminates a conditional block, removing the value from the
  // conditional execution stack.
  //
  // An error is returned if there has not already been a matching OP_IF.
  //
  // Conditional stack transformation: [... OpCondValue] -> [...]