Fix - correctly use central canvas defs for fill patterns

If by chance defs was created in other place, fill pattern was attached
to wrong place

Author: linev

scripts/JSRootPainter.js

@@ -1864,9 +1864,9 @@
 
          var id = "pat_" + this.pattern + "_" + this.colorindx;
 
-         var defs = svg.select('defs');
+         var defs = svg.select('.canvas_defs');
          if (defs.empty())
-            defs = svg.insert("svg:defs",":first-child");
+            defs = svg.insert("svg:defs",":first-child").attr("class","canvas_defs");
 
          var line_color = this.color;
          this.color = "url(#" + id + ")";