Fix strict javascript warning in CanvasGraphics.

pdf.js

@@ -5649,7 +5649,8 @@ var CanvasGraphics = (function canvasGraphics() {
       var tmpCtx = tmpCanvas.getContext('2d');
       if (imageObj.imageMask) {
         var fillColor = this.current.fillColor;
-        tmpCtx.fillStyle = (fillColor && fillColor.type === 'Pattern') ?
+        tmpCtx.fillStyle = (fillColor && fillColor.hasOwnProperty('type') &&
+                            fillColor.type === 'Pattern') ?
                             fillColor.getPattern(tmpCtx) : fillColor;
         tmpCtx.fillRect(0, 0, w, h);
       }