Change static to const since it-stability is not guaranteed

[Kilidsch]

In pcl::visualization::PCLVisualizer::resetCameraViewpoint an iterator of a std::unordered_map was saved in a static variable, even though it might get invalidated when rehashing occurs (see https://en.cppreference.com/w/cpp/container/unordered_map ).

The function also always uses the first id it was ever passed, essentially ignoring the param after the first call.

(NOTE: I am not sure, if the space between find and parantheses was intentional. If yes, I'll recreate it)

[mvieth]

Thanks!
Regarding the space after find: We are slowly enforcing uniform formatting via clang-format, module-by-module. For visualization, formatting is not enforced yet, but the formatting rules say that there should not be a space between function name and parentheses. So deleting it is perfectly fine 🙂