Fix spamming errors when SoftBody pinned nodes have no attachment

There was a specific case where the node path wasn't checked for
validity before trying to access the attachment node.

It could cause lots of error log noise in both editor and game.

scene/3d/soft_body.cpp

@@ -785,8 +785,11 @@ void SoftBody::_reset_points_offsets() {
 	PoolVector<PinnedPoint>::Write w = pinned_points.write();
 	for (int i = pinned_points.size() - 1; 0 <= i; --i) {
 
-		if (!r[i].spatial_attachment)
-			w[i].spatial_attachment = Object::cast_to<Spatial>(get_node(r[i].spatial_attachment_path));
+		if (!r[i].spatial_attachment) {
+			if (!r[i].spatial_attachment_path.is_empty() && has_node(r[i].spatial_attachment_path)) {
+				w[i].spatial_attachment = Object::cast_to<Spatial>(get_node(r[i].spatial_attachment_path));
+			}
+		}
 
 		if (!r[i].spatial_attachment)
 			continue;