Fix duplication of codeblock elements

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/components/views/messages/TextualBody.js

@@ -96,6 +96,9 @@ export default class TextualBody extends React.Component {
             const pres = ReactDOM.findDOMNode(this).getElementsByTagName("pre");
             if (pres.length > 0) {
                 for (let i = 0; i < pres.length; i++) {
+                    // If there already is a div wrapping the codeblock we want to skip this.
+                    // This happens after the codeblock was edited.
+                    if (pres[i].parentNode.className == "mx_EventTile_pre_container") continue;
                     // Wrap a div around <pre> so that the copy button can be correctly positioned
                     // when the <pre> overflows and is scrolled horizontally.
                     const div = this._wrapInDiv(pres[i]);