V4L/DVB (5869): Add check for valid control ID to v4l2_ctrl_next.

If v4l2_ctrl_next is called without the V4L2_CTRL_FLAG_NEXT_CTRL then it 
should check whether the passed control ID is valid and return 0 if it 
isn't. Otherwise a for-loop over the control IDs will never end.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/v4l2-common.c

@@ -939,16 +939,25 @@ int v4l2_ctrl_query_menu(struct v4l2_querymenu *qmenu, struct v4l2_queryctrl *qc
    When no more controls are available 0 is returned. */
 u32 v4l2_ctrl_next(const u32 * const * ctrl_classes, u32 id)
 {
-	u32 ctrl_class;
+	u32 ctrl_class = V4L2_CTRL_ID2CLASS(id);
 	const u32 *pctrl;
 
-	/* if no query is desired, then just return the control ID */
-	if ((id & V4L2_CTRL_FLAG_NEXT_CTRL) == 0)
-		return id;
 	if (ctrl_classes == NULL)
 		return 0;
+
+	/* if no query is desired, then check if the ID is part of ctrl_classes */
+	if ((id & V4L2_CTRL_FLAG_NEXT_CTRL) == 0) {
+		/* find class */
+		while (*ctrl_classes && V4L2_CTRL_ID2CLASS(**ctrl_classes) != ctrl_class)
+			ctrl_classes++;
+		if (*ctrl_classes == NULL)
+			return 0;
+		pctrl = *ctrl_classes;
+		/* find control ID */
+		while (*pctrl && *pctrl != id) pctrl++;
+		return *pctrl ? id : 0;
+	}
 	id &= V4L2_CTRL_ID_MASK;
-	ctrl_class = V4L2_CTRL_ID2CLASS(id);
 	id++;	/* select next control */
 	/* find first class that matches (or is greater than) the class of
 	   the ID */