Fix all controls showing with nothing selected

Fixes #11

src/panel/PropertiesPanel.tsx

@@ -77,17 +77,25 @@ const ControlCondition: React.FC<ControlConditionProps> = ({ objects, test, cont
     return isValid ? <Control objects={objects} /> : null;
 };
 
+const NoObjectsMessage: React.FC = () => {
+    return <p>No objects selected.</p>;
+};
+
 const Controls: React.FC = () => {
     const classes = useControlStyles();
     const [selection] = useSelection();
     const step = useCurrentStep();
 
     if (selection.size === 0) {
-        return <p>No objects selected.</p>;
+        return <NoObjectsMessage />;
     }
 
     const objects = getSelectedObjects(step, selection);
 
+    if (objects.length === 0) {
+        return <NoObjectsMessage />;
+    }
+
     return (
         <>
             <ControlCondition objects={objects} test={isNamed} control={NameControl} />