iOS: Guard against UIGestureRecognizer messing with self

We pass in self to initWithTarget, so we need to be sure that the
init doesn't return a new self.

Change-Id: I90d0d10d2fd1a5d38ef1ff3f23169dcce00b28e2
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@theqtcompany.com>

src/plugins/platforms/ios/qiosinputcontext.mm

@@ -74,7 +74,10 @@ static QUIView *focusView()
 
 - (id)initWithQIOSInputContext:(QIOSInputContext *)context
 {
+    id originalSelf = self;
     if (self = [super initWithTarget:self action:@selector(gestureStateChanged:)]) {
+        Q_ASSERT(self == originalSelf);
+
         m_context = context;
 
         // UIGestureRecognizer