Fix: Node operators crash when using depsgraph

The scene time node and volume nodes crashed, since the despgraph
needs to be retrieved from the operator data instead of modifier data.

source/blender/nodes/NOD_geometry_exec.hh

@@ -217,6 +217,9 @@ class GeoNodeExecParams {
       if (data->modifier_data) {
         return data->modifier_data->depsgraph;
       }
+      if (data->operator_data) {
+        return data->operator_data->depsgraph;
+      }
     }
     return nullptr;
   }