Fix missing initialization of colors settings of a board, when created by a python script.

A pointer was not initialized, therefore plots from a python script sometimes crash.

Fixes: lp:1721166
https://bugs.launchpad.net/kicad/+bug/1721166

pcbnew/plot_brditems_plotter.cpp

@@ -57,8 +57,12 @@
 COLOR4D BRDITEMS_PLOTTER::getColor( LAYER_NUM aLayer )
 {
     COLOR4D color = m_board->Colors().GetLayerColor( ToLAYER_ID( aLayer ) );
+
+    // A hack to avoid plotting ahite itmen in white color, expecting the paper
+    // is also white: use a non white color:
     if( color == COLOR4D::WHITE )
         color = COLOR4D( LIGHTGRAY );
+
     return color;
 }