Requiring goal to contain only one statement.

Previously, the parser read the first statement of the goal as its
precondition, but didn’t check that it was properly terminated with a
closing parenthesis. This allowed arbitrary text to be included within
the goal description without error, which was incorrect.

This commit fixes this issue and adds a corresponding unit test.

lib/pddl/src/pddl/detail/parsing/Problem.cpp

@@ -283,6 +283,7 @@ void ProblemParser::parseGoalSection(ast::Problem &problem)
 	VariableStack variableStack;
 
 	problem.goal = parsePrecondition(m_context, astContext, variableStack);
+	tokenizer.expect<std::string>(")");
 
 	skipSection(tokenizer);
 }