fix: add placeholder when grid has no filters

otherwise tools section doesn't get pushed to the right

src/wuttaweb/templates/grids/vue_template.mako

@@ -89,6 +89,9 @@
 
             </div>
           </form>
+
+      % else:
+          <div></div>
       % endif
 
       <div style="display: flex; flex-direction: column; justify-content: space-between;">