fix typo and two small bugs claude found

Author: MjnMixael

code/missioneditor/sexp_tree_model.cpp

@@ -147,7 +147,7 @@ SexpTreeEditorInterface::SexpTreeEditorInterface(const flagset<TreeFlags>& flags
 SexpTreeEditorInterface::~SexpTreeEditorInterface() = default;
 
 // Returns true if mission-specific (non-builtin) messages exist.
-bool SexpTreeEditorInterface::hasDefaultMessageParamter()
+bool SexpTreeEditorInterface::hasDefaultMessageParameter()
 {
 	return Num_messages > Num_builtin_messages;
 }
@@ -397,6 +397,7 @@ void SexpTreeModel::free_node2(int node)
 	if (modified)
 		*modified = 1;
 	tree_nodes[node].type = SEXPT_UNUSED;
+	tree_nodes[node].handle = nullptr;
 	total_nodes--;
 
 	// Remove any annotation referencing this node so that if allocate_node()
@@ -934,7 +935,7 @@ int SexpTreeModel::query_false(int node) const
 // Look for the valid operator that is the closest match for 'str' and return the operator
 // number of it.  What operators are valid is determined by 'node', and an operator is valid
 // if it is allowed to fit at position 'node'
-const SCP_string& SexpTreeModel::match_closest_operator(const SCP_string& str, int node) const
+SCP_string SexpTreeModel::match_closest_operator(const SCP_string& str, int node) const
 {
 	int z, op, arg_num, opf;
 

code/missioneditor/sexp_tree_model.h

@@ -170,7 +170,7 @@ class SexpTreeEditorInterface {
 	virtual ~SexpTreeEditorInterface();
 
 	// Returns true if there are mission-specific (non-builtin) messages available
-	virtual bool hasDefaultMessageParamter();
+	virtual bool hasDefaultMessageParameter();
 	// Returns the list of mission-specific message names
 	virtual SCP_vector<SCP_string> getMessages();
 
@@ -510,7 +510,7 @@ class SexpTreeModel {
 	// Return TRUE if the root operator is OP_FALSE
 	int query_false(int node = -1) const;
 	// Find the valid operator whose name most closely matches 'str' at position 'node'
-	const SCP_string& match_closest_operator(const SCP_string& str, int node) const;
+	SCP_string match_closest_operator(const SCP_string& str, int node) const;
 	// Look up the help text string for the given sexp operator code
 	static const char* help(int code);
 	// Search all editable nodes for matching text; populates 'find' array, returns match count

code/missioneditor/sexp_tree_opf.cpp

@@ -2762,7 +2762,7 @@ int SexpTreeOPF::query_default_argument_available(int op, int i) const
 		}
 
 		case OPF_MESSAGE:
-			if (_model._interface && _model._interface->hasDefaultMessageParamter())
+			if (_model._interface && _model._interface->hasDefaultMessageParameter())
 				return 1;
 
 			return 0;

qtfred/src/ui/dialogs/MissionEventsDialog.cpp

@@ -227,7 +227,7 @@ SCP_vector<SCP_string> MissionEventsDialog::getMessages()
 	return out;
 }
 
-bool MissionEventsDialog::hasDefaultMessageParamter()
+bool MissionEventsDialog::hasDefaultMessageParameter()
 {
 	return !_model->getMessageList().empty();
 }

qtfred/src/ui/dialogs/MissionEventsDialog.h

@@ -31,7 +31,7 @@ class MissionEventsDialog: public QDialog, public SexpTreeEditorInterface {
 	void reject() override;
 
 	SCP_vector<SCP_string> getMessages() override;
-	bool hasDefaultMessageParamter() override;
+	bool hasDefaultMessageParameter() override;
 	int getRootReturnType() const override;
 
   protected: