Update WhiteRectangleDetector.java

Changed image-only version of the constructor to calculate an appropriate initSize based on the image dimensions.
Modified WhiteRectangleDetector

Continue expanding the rectangle until at least one black point has been
found on each side, instead of stopping immediately when all sides are
white - which might still be inside the barcode.
Merge pull request #52 from tgibson11/master

Reduce possibility of detecting white rectangles within barcodes