UI: fix display of menu buttons without text and icon, and only a down arrow.

Differential Revision: https://developer.blender.org/D4123

source/blender/editors/interface/interface_layout.c

@@ -291,6 +291,9 @@ static int ui_text_icon_width(uiLayout *layout, const char *name, int icon, bool
 	variable = ui_layout_variable_size(layout);
 
 	if (variable) {
+		if (!icon && !name[0]) {
+			return unit_x; /* No icon or name. */
+		}
 		if (layout->alignment != UI_LAYOUT_ALIGN_EXPAND) {
 			layout->item.flag |= UI_ITEM_MIN;
 		}