Merge pull request #79 from ale-cci/fix/issue_74

Init tempCanvasElement to null

Author: werthdavid

src/common/HTMLCanvasElementLuminanceSource.ts

@@ -43,7 +43,7 @@ export class HTMLCanvasElementLuminanceSource extends LuminanceSource {
 
   private buffer: Uint8ClampedArray;
 
-  private tempCanvasElement?: HTMLCanvasElement;
+  private tempCanvasElement?: HTMLCanvasElement = null;
 
   public constructor(private canvas: HTMLCanvasElement) {
     super(canvas.width, canvas.height);