Insert transparent gif if img does not have src attribute

Thus it will prevent invalid value to be inserted when trying to fix img
tags.

Before this change the line:

  <img alt="Hello world">

led to:

  <img alt="Hello world" src="src">

Now, the src attribute will be initialized with the value:

  data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==

Signed-off-by: Kevin Decherf <kevin@kdecherf.com>

Author: Kdecherf

htmLawed.php

@@ -874,7 +874,7 @@ function hl_tag($t)
     }
 
     // rqd attr
-    static $eAR = ['area' => ['alt' => 'area'], 'bdo' => ['dir' => 'ltr'], 'command' => ['label' => ''], 'form' => ['action' => ''], 'img' => ['src' => '', 'alt' => 'image'], 'map' => ['name' => ''], 'optgroup' => ['label' => ''], 'param' => ['name' => ''], 'style' => ['scoped' => ''], 'textarea' => ['rows' => '10', 'cols' => '50']];
+    static $eAR = ['area' => ['alt' => 'area'], 'bdo' => ['dir' => 'ltr'], 'command' => ['label' => ''], 'form' => ['action' => ''], 'img' => ['src' => 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==', 'alt' => 'image'], 'map' => ['name' => ''], 'optgroup' => ['label' => ''], 'param' => ['name' => ''], 'style' => ['scoped' => ''], 'textarea' => ['rows' => '10', 'cols' => '50']];
     if (isset($eAR[$e])) {
         foreach ($eAR[$e] as $k => $v) {
             if (!isset($a[$k])) {