Checking for existence in `std::map` - `count` vs `find`

Currently we are using a lot of iterators just to check if an element exists in a map, like here:
https://github.com/PointCloudLibrary/pcl/blob/f9f214f34a38d5bb67441140703a681c5d299906/visualization/src/pcl_visualizer.cpp#L3261-L3268

To increase readability we have two options:
Option 1) Use auto

  auto am_it = cloud_actor_map_->find (id);
  if (am_it != cloud_actor_map_->end ())
  ...

Option 2) As single line:

  if (cloud_actor_map_->find (id) != cloud_actor_map_->end ())
  ...

Option 3) With count (complexity is logarithmic like find)

  if (cloud_actor_map_->count (id) > 0)
  ...

See similar discussion on StackOverflow.

Pro/Cons:

• Option 1) iterator variable is longer valid as necessary
• Option 2) In case of a long variable name we may reach the maximum line length defined by clang-format => line break
• Option 3) Shortest and imho best to read, but performance maybe be a few CPU ticks slower (GCC should be equal, but MSVC not sure)

So prefer performance or readability?

Start at visualization/src/pcl_visualizer.cpp lines 3261-3268 and review the linked discussion of find versus count. Compare the proposed styles and their readability and performance trade-offs, then define the project-wide preference; done means the choice and its scope are agreed upon.