fix: conclusion field only accepts one clue

modules/you_done_it/conclusion_field.cpp

@@ -17,6 +17,9 @@ void ConclusionField::enter_tree() {
 }
 
 void ConclusionField::on_body_entered(Node2D *node) {
+	if (this->photo) {
+		return; // only accept one photo at a time
+	}
 	if (PinnedPhoto * photo{ cast_to<PinnedPhoto>(node) }) {
 		photo->push_conclusion_slot(this);
 	}