Utils: Set TipContent pointer to null in destructor.

Task-number: QTCREATORBUG-8582

Change-Id: I29e875564d983c4a1154cbc962616e1488425ac3
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/texteditor/tooltip/tips.cpp

@@ -72,7 +72,9 @@ QTipLabel::QTipLabel(QWidget *parent) :
 
 QTipLabel::~QTipLabel()
 {
-    delete m_tipContent;
+    Utils::TipContent *tmpTipContent = m_tipContent;
+    m_tipContent = 0;
+    delete tmpTipContent;
 }
 
 bool QTipLabel::isInteractive() const