Eeschema, DIALOG_PLOT_SCHEMATIC: fix incorrect unit of default pen width.

The default line width used to set the  default pen width is given in mils,
and the conversion to iu was missing.
Fix also a minor Coverity warning.

Fixes #4594
https://gitlab.com/kicad/code/kicad/issues/4594

pcbnew/pcb_plot_params.cpp

@@ -147,6 +147,8 @@ PCB_PLOT_PARAMS::PCB_PLOT_PARAMS()
     // it is a "local" parameter
     m_skipNPTH_Pads              = false;
 
+    m_sketchPadLineWidth         = Millimeter2iu( 0.1 );    // line width to plot items in outline mode
+
     if( PgmOrNull() )
     {
         SETTINGS_MANAGER& mgr = Pgm().GetSettingsManager();