router: use actual snap point position for routability checks of a segment instead of the segment endpoint(s).

Explanation:
- place a long segment A with something violating the rules close to its endpoint
- try to start routing in the 2/3 of the length of A (on the obstacle side)
- bummer - the router picks the nearest endpoint of A for the collision check (even though we don't care about this collision since we want to route far away from it)

(cherry picked from commit e558893851)

pcbnew/router/pns_node.cpp

@@ -484,7 +484,7 @@ NODE::OPT_OBSTACLE NODE::CheckColliding( const ITEM* aItemA, int aKindMask )
         if( line->EndsWithVia() )
         {
             n += QueryColliding( &line->Via(), obs, aKindMask, 1 );
-
+            
             if( n )
                 return OPT_OBSTACLE( obs[0] );
         }

pcbnew/router/pns_router.cpp

@@ -273,18 +273,7 @@ bool ROUTER::isStartingPointRoutable( const VECTOR2I& aWhere, ITEM* aStartItem,
         }
     }
 
-    VECTOR2I startPoint = aStartItem ? aStartItem->Anchor( 0 ) : aWhere;
-
-    if( aStartItem && aStartItem->OfKind( ITEM::SEGMENT_T | ITEM::ARC_T ) )
-    {
-        VECTOR2I otherEnd = aStartItem->Anchor( 1 );
-
-        if( ( otherEnd - aWhere ).SquaredEuclideanNorm()
-                < ( startPoint - aWhere ).SquaredEuclideanNorm() )
-        {
-            startPoint = otherEnd;
-        }
-    }
+    VECTOR2I startPoint = aWhere;
 
     if( m_mode == PNS_MODE_ROUTE_SINGLE )
     {