pcbnew: properly close tags when handling bad poly

The parenthesis depth is 2 when the polygon isn't closed.  This
shouldn't happen but we have the fall-through to handle odd cases

Fixes: lp:1844872
* https://bugs.launchpad.net/kicad/+bug/1844872

(cherry picked from commit d862cdaa72)

pcbnew/kicad_plugin.cpp

@@ -1875,8 +1875,13 @@ void PCB_IO::format( ZONE_CONTAINER* aZone, int aNestLevel ) const
         }
 
         if( !is_closed )    // Should not happen, but...
-            m_out->Print( aNestLevel+1, ")\n" );
+        {
+            if( newLine != 0 )
+                m_out->Print( 0, "\n" );
 
+            m_out->Print( aNestLevel+2, ")\n" );
+            m_out->Print( aNestLevel+1, ")\n" );
+        }
     }
 
     // Save the PolysList (filled areas)