fix segfault on unavailable previous result use

alib2cli/src/ast/statements/PreviousResultStatement.h

@@ -9,6 +9,8 @@ class PreviousResultStatement final : public Statement {
 public:
 	virtual std::shared_ptr < abstraction::OperationAbstraction > translateAndEval ( const std::shared_ptr < abstraction::OperationAbstraction > & prev, Environment & ) const override {
+		if ( prev == nullptr )
+			throw std::invalid_argument ( "There is no previous result to use." );
 		return prev;
 	}