Fix display of project/platform cross-ref adjustments

We were trying to use the in-file calculation for an external
address, so the adjustment was always zero.

Also, don't pass a fill brush for wireframe rendering.  (No change
in behavior.)

SourceGen/DisasmProject.cs

@@ -1541,9 +1541,8 @@ namespace SourceGen {
                                     sym.SymbolSource == Symbol.Source.Platform) {
                                 DefSymbol defSym = sym as DefSymbol;
                                 int adj = 0;
-                                if (operandOffset >= 0) {
-                                    adj = defSym.Value - operandOffset;
-                                }
+                                Debug.Assert(operandOffset < 0);    // outside file scope
+                                adj = defSym.Value - attr.OperandAddress;
                                 defSym.Xrefs.Add(
                                     new XrefSet.Xref(offset, true, xrefType, accType, adj));
                             } else {

SourceGen/Visualization.cs

@@ -311,7 +311,7 @@ namespace SourceGen {
             using (DrawingContext dc = dv.RenderOpen()) {
                 dc.DrawRectangle(Brushes.Black, null, new Rect(0, 0, bounds.Width, bounds.Height));
                 Pen pen = new Pen(Brushes.White, 1.0);
-                dc.DrawGeometry(Brushes.White, pen, geo);
+                dc.DrawGeometry(null, pen, geo);
             }
             bitmap.Render(dv);