chatview: hide the message bar scrollbars if there is no content

Gitlab: #978
Change-Id: Ifdc7306c6082c93f74fcb3e8472405d326faea74

src/app/mainview/components/MessageBarTextArea.qml

@@ -31,6 +31,9 @@ JamiFlickable {
     property var textAreaObj: textArea
     property alias placeholderText: textArea.placeholderText
 
+    ScrollBar.vertical.visible: textArea.text
+    ScrollBar.horizontal.visible: textArea.text
+
     signal sendMessagesRequired
 
     function insertText(text) {