Fix gcc11 warning

[zanaviska]

‘error’ may be used uninitialized.
We used to declare error uninitialized, pass it to LineFit as OUT parameter, hoping that every path will initialize error varible. But there is path, where error is kept uninitialized, so it is better to explicitly initialize it here

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• I agree to contribute to the project under Apache 2 License.
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  Patch to opencv_extra has the same branch name.
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[zanaviska]

There may be clang-tidy warning about reducing scope of the variable, but I decided that it goes outside of the change that I was trying to make, since I was just trying to get rid of console warning. If maintainers think, that I should reduce variable scope too, write here about it

[asmorkalov]

👍