pcbnew: Prevent degenerate values in Eagle import

Importing Eagle files allowed for invalid zone values for clearance and
minimum width that triggered asserts in the 3d-viewer.

Fixes: lp:1801188
* https://bugs.launchpad.net/kicad/+bug/1801188

3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp

@@ -752,8 +752,9 @@ void CINFO3D_VISU::AddShapeWithClearanceToContainer( const DRAWSEGMENT* aDrawSeg
                                                      PCB_LAYER_ID aLayerId,
                                                      int aClearanceValue )
 {
-    // The full width of the lines to create:
-    const int linewidth = aDrawSegment->GetWidth() + (2 * aClearanceValue);
+    // The full width of the lines to create
+    // The extra 1 protects the inner/outer radius values from degeneracy
+    const int linewidth = aDrawSegment->GetWidth() + (2 * aClearanceValue) + 1;
 
     switch( aDrawSegment->GetShape() )
     {

pcbnew/eagle_plugin.cpp

@@ -1174,7 +1174,8 @@ ZONE_CONTAINER* EAGLE_PLUGIN::loadPolygon( wxXmlNode* aPolyNode )
 
     // clearances, etc.
     zone->SetArcSegmentCount( 32 );     // @todo: should be a constructor default?
-    zone->SetMinThickness( p.width.ToPcbUnits() );
+    zone->SetMinThickness( std::max<int>(
+            ZONE_THICKNESS_MIN_VALUE_MIL*IU_PER_MILS, p.width.ToPcbUnits() ) );
 
     // FIXME: KiCad zones have very rounded corners compared to eagle.
     //        This means that isolation amounts that work well in eagle
@@ -1182,7 +1183,7 @@ ZONE_CONTAINER* EAGLE_PLUGIN::loadPolygon( wxXmlNode* aPolyNode )
     if( p.isolate )
         zone->SetZoneClearance( p.isolate->ToPcbUnits() );
     else
-        zone->SetZoneClearance( 0 );
+        zone->SetZoneClearance( 1 ); // @todo: set minimum clearance value based on board settings
 
     // missing == yes per DTD.
     bool thermals = !p.thermals || *p.thermals;