fix(layout): Prevent class overriding when lastClass is null

This fixes an annoying behavior of the layout attributes that is removing all the element's other classes when trying to convert layout attributes to classes.

Closes #5257.

Author: mallowigi

src/core/services/layout/layout.js

@@ -322,8 +322,10 @@
     return function updateClassFn(newValue) {
       var value = validateAttributeValue(className, newValue || "");
       if ( angular.isDefined(value) ) {
-        element.removeClass(lastClass);
-        lastClass = !value ? className : className + "-" + value.replace(WHITESPACE, "-")
+        if (lastClass) { 
+          element.removeClass(lastClass);
+        }
+        lastClass = !value ? className : className + "-" + value.replace(WHITESPACE, "-");
         element.addClass(lastClass);
       }
     };