Only queue connectedMoveCallback if connected

Initially, we could unconditionally queue the connectedMoveCallback,
because `moveBefore()` only worked when the origin and destination were
both connected. After
2bbc834,
we support the disconnected->disconnected case, which means we have to
explicitly gate this step on being connected.

dom.bs

@@ -2982,9 +2982,10 @@ before a <var>child</var>, run these steps:
     <a>insertion steps</a> or <a>removing steps</a> for <var>inclusiveDescendant</var>.
    </li>
 
-   <p>If <var>inclusiveDescendant</var> is <a for=Element>custom</a>, then
-   <a>enqueue a custom element callback reaction</a> with <var>inclusiveDescendant</var>, callback
-   name "<code>connectedMoveCallback</code>", and an empty argument list.
+   <p>If <var>inclusiveDescendant</var> is <a for=Element>custom</a> and <var>newParent</var> is
+   <a>connected</a>, then <a>enqueue a custom element callback reaction</a> with
+   <var>inclusiveDescendant</var>, callback name "<code>connectedMoveCallback</code>", and an empty
+   argument list.
 
    <li>
     <p>Otherwise, <a lt="try to upgrade an element">try to upgrade</a>