Fix T89775: geometry nodes logging crash during render

Under some circumstances (e.g. when rendering) the geometry
nodes logger is not used. This was missing a simple null check.

source/blender/nodes/intern/node_geometry_exec.cc

@@ -30,6 +30,9 @@ namespace blender::nodes {
 
 void GeoNodeExecParams::error_message_add(const NodeWarningType type, std::string message) const
 {
+  if (provider_->logger == nullptr) {
+    return;
+  }
   LocalGeoLogger &local_logger = provider_->logger->local();
   local_logger.log_node_warning(provider_->dnode, type, std::move(message));
 }