Editor: Fix crash when trying to save scenario into itself

planet/System.ocg/LanguageDE.txt

@@ -87,6 +87,7 @@ IDS_CNS_PLRQUITNET=%s (%s) löschen
 IDS_CNS_PROPERTIES=Eigenschaften
 IDS_CNS_REMOVE=Entfernen
 IDS_CNS_SAVEASERROR=Fehler beim Speichern des Szenarios nach %s.
+IDS_CNS_RECURSIVESAVEASERROR=Speichern in das existierende Szenario ist nicht möglich. Bitte neuen Pfad wählen.
 IDS_CNS_SAVERROR=Fehler beim Speichern des Szenarios.
 IDS_CNS_SCENARIOFILE=OpenClonk Szenariendatei
 IDS_CNS_SCENARIOSAVED=Szenario gespeichert.

planet/System.ocg/LanguageUS.txt

@@ -87,6 +87,7 @@ IDS_CNS_PLRQUITNET=Remove %s (%s)
 IDS_CNS_PROPERTIES=Properties
 IDS_CNS_REMOVE=Remove
 IDS_CNS_SAVEASERROR=Error while saving the scenario to %s.
+IDS_CNS_RECURSIVESAVEASERROR=Cannot save into the existing scenario. Please choose another path.
 IDS_CNS_SAVERROR=Error while saving the scenario.
 IDS_CNS_SCENARIOFILE=OpenClonk scenario file
 IDS_CNS_SCENARIOSAVED=Scenario saved.

src/editor/C4Console.cpp

@@ -178,6 +178,14 @@ bool C4Console::SaveScenario(const char * path, bool export_packed)
 	}
 	else if (path)
 	{
+		// When trying to save into a subfolder of the existing scenario, the copy function
+		// below will try to recursively copy everything until it blows the stack. There is
+		// really no good reason to do this, so we just disallow it here.
+		if (SEqual2(path, Game.ScenarioFilename))
+		{
+			Message(LoadResStr("IDS_CNS_RECURSIVESAVEASERROR"));
+			return false;
+		}
 		// Open new scenario file
 		// Close current scenario file to allow re-opening at new path
 		Game.ScenarioFile.Close();