Fix regression in iframe/frame loading

Closes #6168. This was due to a boolean logic error in the refactoring
performed in f283972.

source

@@ -30199,12 +30199,15 @@ interface <dfn>HTMLIFrameElement</dfn> : <span>HTMLElement</span> {
     </ol>
    </li>
 
-   <li><p>Otherwise, if <var>initialInsertion</var> is false, run the <span>otherwise steps for
-   <code>iframe</code> or <code>frame</code> elements</span> given <var>element</var>.</p></li>
+   <li><p>Otherwise, if <var>element</var> has a <code data-x="attr-iframe-src">src</code> attribute
+   specified, or <var>initialInsertion</var> is false, then run the <span>shared attribute
+   processing steps for <code>iframe</code> and <code>frame</code> elements</span> given
+   <var>element</var>.</p></li>
   </ol>
 
-  <p>The <dfn>otherwise steps for <code>iframe</code> or <code>frame</code> elements</dfn>, given an
-  element <var>element</var>, are:</p>
+  <p id="otherwise-steps-for-iframe-or-frame-elements">The <dfn>shared attribute processing steps
+  for <code>iframe</code> and <code>frame</code> elements</dfn>, given an element
+  <var>element</var>, are:</p>
 
   <ol>
    <li>
@@ -118673,10 +118676,10 @@ interface <dfn>HTMLFrameSetElement</dfn> : <span>HTMLElement</span> {
   data-x="process-frame-initial-insertion"><var>initialInsertion</var></dfn>:</p>
 
   <ol>
-   <li><p>If <var>initialInsertion</var> is true, then do nothing.</p></li>
-
-   <li><p>Otherwise, run the <span>otherwise steps for <code>iframe</code> or <code>frame</code>
-   elements</span> given <var>element</var>.</p></li>
+   <li><p>If <var>element</var> has a <code undefined data-x="attr-frame-src">src</code> attribute
+   specified, or <var>initialInsertion</var> is false, then run the <span>shared attribute
+   processing steps for <code>iframe</code> and <code>frame</code> elements</span> given
+   <var>element</var>.</p></li>
   </ol>
 
   <p>The <code>frame</code> element <span>potentially delays the load event</span>.</p>