Fix: Adding new 3D View changes custom transform orientation to gimbal

Steps to recreate were:
* Create custom transform orientation.
* Change properties editor into 3D View.
* Trigger refresh of 3D view header by mouse hovering it.

Mistake in rB7d055da327b9555f.

source/blender/editors/space_view3d/space_view3d.c

@@ -358,8 +358,7 @@ static SpaceLink *view3d_new(const bContext *C)
 
 	v3d->twflag |= U.manipulator_flag & V3D_MANIPULATOR_DRAW;
 	v3d->around = V3D_AROUND_CENTER_MEAN;
-	scene->orientation_index_custom = -1;
-	
+
 	v3d->bundle_size = 0.2f;
 	v3d->bundle_drawtype = OB_PLAINAXES;