fix Aztec decode: white-fill canvas before drawImage so transparent quiet-zone pixels composite to white instead of packing as black in ZXing ARGB

@@ -174,6 +174,12 @@174174     const canvas = new OffscreenCanvas(bitmap.width, bitmap.height);175175     const ctx = canvas.getContext("2d");176176     if (!ctx) return null;177+    // White-fill before drawing so any transparent pixels in the PNG178+    // composite to white rather than (0,0,0,0). Transparent pixels get179+    // packed as 0xFF000000 (black) in the ARGB array, which would make180+    // the quiet-zone border appear black and confuse ZXing.181+    ctx.fillStyle = "#ffffff";182+    ctx.fillRect(0, 0, bitmap.width, bitmap.height);177183     ctx.drawImage(bitmap, 0, 0);178184     const imageData = ctx.getImageData(0, 0, bitmap.width, bitmap.height);179185