Fix cppcheck reports warnings:

(performance) Possible inefficient checking for 'lmap' emptiness
(warning) Assignment of function parameter has no effect outside the function. Did you forget dereferencing it?
(style) Array index '<xxx>' is used before limits check

modules/imgproc/src/shapedescr.cpp

@@ -79,7 +79,7 @@ static bool findCircle( Point2f pt0, Point2f pt1, Point2f pt2,
     }
 
     center->x = center->y = 0.f;
-    radius = 0;
+    *radius = 0;
     return false;
 }