Resize the legend area when traces are hidden

The legend area is determined using the legends of all the traces
even if they are not being displayed. This fix addresses that by
only considering the visible traces.

applications/appunorganized/appunorganized-plugins/org.csstudio.swt.rtplot/src/org/csstudio/swt/rtplot/internal/LegendPart.java

@@ -66,22 +66,25 @@ public int getDesiredHeight(final GC gc, final int bounds_width,
         final Font orig_font = gc.getFont();
         gc.setFont(font);
 
+        int items = 0;
         int max_width = 1, max_height = 1; // Start with 1 pixel to avoid later div-by-0
         for (Trace<XTYPE> trace : traces)
         {
+            if (!trace.isVisible())
+                continue;
             final Point size = gc.textExtent(trace.getLabel());
             if (size.x > max_width)
                 max_width = size.x;
             if (size.y > max_height)
                 max_height = size.y;
+            items++;
         }
         // Arrange in grid with some extra space
         grid_x = max_width + max_height / 2;
         grid_y = max_height;
 
         gc.setFont(orig_font);
 
-        final int items = traces.size();
         final int items_per_row = Math.max(1, bounds_width / grid_x); // Round down, counting full items
         final int rows = (items + items_per_row-1) / items_per_row;   // Round up
         return rows * grid_y;