‘error’ may be used uninitialized

…n-edge-drawing

Fix gcc11 warning

add maxconers and mindistance setter to gftt

Fix a bug in knnMatchConvert when a feature couldn't be matched opencv#3632

After I started using a mask with `knnMatchAsync`, I found that the result from `knnMatchConvert` would be clipped at random.

Investigating the issue, I found that `knnMatchAsync` will initialize all `trainIdx` to `-1`, which will be overwritten by the CUDA kernel. A mask can be used to prevent certain features from being matched and this will prevent the CUDA kernel from setting the match distance. `knnMatchConvert` is not properly incrementing the pointers when `trainIdx == -1`, so an unmatched feature will get it stuck at `if (trainIdx == -1)`. Eventually the outer for-loop finishes and returns a vector with the matches up until the first missing match distance.

My solution is to increment the counters the same way as a successful iteration would.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake