Improve callable value handling

Changed:
- Check if value is callable instead of just a `Closure` to support invokable objects.
- Moved callable value to earlier in case its value is NULL or a special object.

Author: mcaskill

Function.HTML-Build-Attributes.php

@@ -22,10 +22,6 @@ function html_build_attributes($attr, callable $callback = null)
 
         $html = [];
         foreach ($attr as $key => $val) {
-            if (is_null($val)) {
-                continue;
-            }
-
             if (is_string($key)) {
                 $key = trim($key);
 
@@ -34,10 +30,16 @@ function html_build_attributes($attr, callable $callback = null)
                 }
             }
 
+            if (is_callable($val)) {
+                $val = $val();
+            }
+
+            if (is_null($val)) {
+                continue;
+            }
+
             if (is_object($val)) {
-                if ($val instanceof Closure) {
-                    $val = $val();
-                } elseif (is_callable([ $val, 'toArray' ])) {
+                if (is_callable([ $val, 'toArray' ])) {
                     $val = $val->toArray();
                 } elseif (is_callable([ $val, '__toString' ])) {
                     $val = strval($val);