Fix weird icon padding in asset library selector menu button

Since the menu doesn't automatically align the labels like other menus
and pulldowns in Blender, I manually made them align using the blank
icon. However the menu button would also include this blank icon now.

This is a specific fix for the 3.5 release. In the main branch I will
replace it with proper support for automatically aligning labels in such
menus.

source/blender/editors/interface/interface.cc

@@ -4585,7 +4585,15 @@ static uiBut *ui_def_but_rna(uiBlock *block,
 #endif
       }
 
-      icon = item[i].icon;
+      /* #ICON_BLANK1 can be used to add padding of the size of an icon. This is fine to align
+       * multiple items within a menu, but not for the menu button that only shows the label then.
+       */
+      if ((type == UI_BTYPE_MENU) && (item[i].icon == ICON_BLANK1)) {
+        icon = ICON_NONE;
+      }
+      else {
+        icon = item[i].icon;
+      }
     }
     else {
       if (!str) {