Mistake in own rBb6a35a8153c3 which caused code to always recurse into
bone hierarchies (no matter which collapsed level an armature was
found).
This led to bone counts always being displayed even outside a collapsed
armature (e.g. if an armature was somewhere down a object or collection,
the collapsed object or collection would show this bonecount).
This is inconsistent with other data counting in the Outliner, e.g.
vertexgroups or bonegroups do have their indicator at object level,
however the counter only shows if Vertex Groups or Bone Groups line
shows (so if the object is not collapsed).

And this also led to the bug reported in T101946 which was that the bone
counts would be treated as collections when further down a collapsed
hierarchy.
Background: The whole concept of MergedIconRow is based on the concept
of counting objects types or collectinons/groups. If other things
like overrides, vertexgroups or bonegroups are displayed in a counted/
merged manner, then these will always be counted in the array spots that
are usually reserved for groups/collections. But for things this is not
a problem (since these are only displayed below their respective
outliner entry -- and will never be reached otherwise).

So to correct all this, we now only recurse into a bone hierarchy if we
started off with an armature data-block (so the first shown thing would
be a "level-zero" bone).