Sanitization on line 1206 breaks first tab xclass

Sanitizing the class name on line 1206

( !empty($class) ) ? ' class="' . sanitize_html_class($class) . '"' : '',

breaks the first table xclass removing the space after “active”.
E.g.:

[tab title="MyTitle" active="true" xclass="myclass"]
results in
<li class="activemyclass">

It worths noting that multiple class names inside the same xclass keep working (e.g. xclass="myclass1 myclass2" results in <li class=" myclass1 myclass2">).

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