Performance Regression with 0.9.0

[mripard]

Hi,

I've updated rqrr to the latest version, and found a pretty noticeable performance drop when decoding a QR code from an image.

I've created a benchmark you can find here: https://github.com/mripard/rqrr/tree/rqrr-decode-frame-bench

On my box, an iteration goes from 3.5ms to 5.5ms on average:

qrcode detection        time:   [5.6411 ms 5.6475 ms 5.6546 ms]
                        change: [+60.041% +60.308% +60.559%] (p = 0.00 < 0.05)
                        Performance has regressed.
Found 11 outliers among 100 measurements (11.00%)
  8 (8.00%) high mild
  3 (3.00%) high severe

[WanzenBug]

I expect this is caused by #30
I don't really have time to look into that right now.