Fixed crash on DRC

Fixes: lp:1650360
* https://bugs.launchpad.net/kicad/+bug/1650360

pcbnew/class_marker_pcb.h

@@ -113,7 +113,8 @@ public:
 
     const BOX2I ViewBBox() const override
     {
-        return m_item->ViewBBox();
+        // The following is based on the PCB_PAINTER::draw( const MARKER_PCB* )
+        return BOX2I( m_Pos, VECTOR2I( 1300000, 1300000 ) );
     }
 
     void ViewGetLayers( int aLayers[], int& aCount ) const override;

pcbnew/pcb_painter.cpp

@@ -1025,7 +1025,9 @@ void PCB_PAINTER::draw( const PCB_TARGET* aTarget )
 
 void PCB_PAINTER::draw( const MARKER_PCB* aMarker )
 {
+    // If you are changing this, update MARKER_PCB::ViewBBox()
     const int scale = 100000;
+
     const VECTOR2D arrow[] = {
         VECTOR2D(  0 * scale,   0 * scale ),
         VECTOR2D(  8 * scale,   1 * scale ),