[core] Fix non-anchored Transform::setAngle

This reverts a line change from b33b2f15, because we explicitely want
the anchor to be invalid.

src/mbgl/map/transform.cpp

@@ -502,7 +502,7 @@ void Transform::rotateBy(const ScreenCoordinate& first, const ScreenCoordinate&
 }
 
 void Transform::setAngle(double angle, const Duration& duration) {
-    setAngle(angle, ScreenCoordinate {}, duration);
+    setAngle(angle, ScreenCoordinate { NAN, NAN }, duration);
 }
 
 void Transform::setAngle(double angle, const ScreenCoordinate& anchor, const Duration& duration) {