c++: fix variable shadowing warning in client code

This should supersede zxing-cpp#837, achieving the same with just one changed line.

core/src/Quadrilateral.h

@@ -153,7 +153,7 @@ bool HaveIntersectingBoundingBoxes(const Quadrilateral<PointT>& a, const Quadril
 template <typename PointT>
 Quadrilateral<PointT> Blend(const Quadrilateral<PointT>& a, const Quadrilateral<PointT>& b)
 {
-	auto dist2First = [c = a[0]](auto a, auto b) { return distance(a, c) < distance(b, c); };
+	auto dist2First = [r = a[0]](auto s, auto t) { return distance(s, r) < distance(t, r); };
 	// rotate points such that the the two topLeft points are closest to each other
 	auto offset = std::min_element(b.begin(), b.end(), dist2First) - b.begin();