Adjust RoomSidePane autosize max width

Set it to the RoomHeader's buttons implicitWidth

harmonyqml/components/Chat/Chat.qml

@@ -87,7 +87,9 @@ HColumnLayout {
 
             function set_width() {
                 width = parent.width * 0.3 < collapseBelow ?
-                        Layout.minimumWidth : Math.min(parent.width * 0.3, 300)
+                        Layout.minimumWidth :
+                        Math.min(parent.width * 0.3,
+                                 roomHeader.buttonsImplicitWidth)
             }
 
             onParentWidthChanged:

harmonyqml/components/Chat/RoomHeader.qml

@@ -6,6 +6,8 @@ HRectangle {
     property string displayName: ""
     property string topic: ""
 
+    property alias buttonsImplicitWidth: viewButtons.implicitWidth
+
     property bool collapseButtons: width < 400
 
     id: roomHeader