Don't break backwards compatibility with unmanaged forwards

Instead of adding new functions to `IForward`, we just allow NULL to be passed to `PushArray` and `PushString`.

core/logic/ForwardSys.cpp

@@ -528,10 +528,17 @@ void CForward::_Int_PushArray(cell_t *inarray, unsigned int cells, int flags)
 
 int CForward::PushArray(cell_t *inarray, unsigned int cells, int flags)
 {
-	/* We don't allow this here */
+	/* Push a reference to the NULL_VECTOR pubvar if NULL was passed. */
 	if (!inarray)
 	{
-		return SetError(SP_ERROR_PARAM);
+		/* Make sure this was intentional. */
+		if (cells == 3)
+		{
+			return PushNullVector();
+		} else {
+			/* We don't allow this here */
+			return SetError(SP_ERROR_PARAM);
+		}
 	}
 
 	if (m_curparam < m_numparams)
@@ -568,6 +575,12 @@ void CForward::_Int_PushString(cell_t *inarray, unsigned int cells, int sz_flags
 
 int CForward::PushString(const char *string)
 {
+	/* Push a reference to the NULL_STRING pubvar if NULL was passed. */
+	if (!string)
+	{
+		return PushNullString();
+	}
+
 	if (m_curparam < m_numparams)
 	{
 		if (m_types[m_curparam] == Param_Any)

core/logic/ForwardSys.h

@@ -55,8 +55,6 @@ public: //IForward
 	virtual unsigned int GetFunctionCount();
 	virtual ExecType GetExecType();
 	virtual int Execute(cell_t *result, IForwardFilter *filter);
-	virtual int PushNullString();
-	virtual int PushNullVector();
 public: //IChangeableForward
 	virtual bool RemoveFunction(IPluginFunction *func);
 	virtual unsigned int RemoveFunctionsOfPlugin(IPlugin *plugin);
@@ -74,6 +72,8 @@ private:
 	CForward(ExecType et, const char *name,
 	         const ParamType *types, unsigned num_params);
 
+	int PushNullString();
+	int PushNullVector();
 	int _ExecutePushRef(IPluginFunction *func, ParamType type, FwdParamInfo *param);
 	void _Int_PushArray(cell_t *inarray, unsigned int cells, int flags);
 	void _Int_PushString(cell_t *inarray, unsigned int cells, int sz_flags, int cp_flags);

core/logic/smn_functions.cpp

@@ -580,7 +580,7 @@ static cell_t sm_CallPushNullVector(IPluginContext *pContext, const cell_t *para
 	}
 	else if (s_pForward)
 	{
-		err = s_pForward->PushNullVector();
+		err = s_pForward->PushArray(NULL, 3);
 	}
 
 	if (err)
@@ -621,7 +621,7 @@ static cell_t sm_CallPushNullString(IPluginContext *pContext, const cell_t *para
 	}
 	else if (s_pForward)
 	{
-		err = s_pForward->PushNullString();
+		err = s_pForward->PushString(NULL);
 	}
 
 	if (err)