gui: fix chat block binding loop breaking rendering

The Item wrapper added in 1cfa424 set height: mainTextEdit.height while
the TextEdit used anchors.fill: parent, so the TextEdit height depended
on the Item height and vice versa. The resulting binding loop collapsed
the block layout into visual garbage. Size the TextEdit from
width: parent.width and let its content height drive the Item.

kde/gui/ChatBlockDelegate.qml

@@ -199,7 +199,7 @@ Column {
 
             TextEdit {
                 id: mainTextEdit
-                anchors.fill: parent
+                width: parent.width
                 text: root.blockRenderedHtml
                 textFormat: Text.RichText
                 selectByMouse: true