Fix: crash when opening file with visible node editor

Caused by rB87fd798ae383a344d51dcbd9f66d5834595bdc5a.

source/blender/editors/space_node/node_edit.cc

@@ -1131,6 +1131,10 @@ bNodeSocket *node_find_indicated_socket(SpaceNode &snode,
 
   snode.edittree->ensure_topology_cache();
   const Span<float2> socket_locations = snode.runtime->all_socket_locations;
+  if (socket_locations.is_empty()) {
+    /* Sockets haven't been drawn yet, e.g. when the file is currently opening. */
+    return nullptr;
+  }
 
   const Span<bNode *> nodes = snode.edittree->all_nodes();
   for (int i = nodes.index_range().last(); i >= 0; i--) {