6da723's change prevents bedcov-iitree-bfs from compiling

[xfengnefx]

Hi,

6da723 (fixes #7) introduced if (max_level < 0) return false; into cpp/IITreeBFS.h , but max_level is only defined & used in the IITree class of cpp/IITree.h ...?

On current head (2fb5a2):

$ make
g++ -g -Wall -O3 -D_USE_BFS -std=c++98 -I.. -I../cpp bedcov-iitree.cpp -lz -o bedcov-iitree-bfs
In file included from bedcov-iitree.cpp:6:
../cpp/IITreeBFS.h: In member function ‘bool IITree<S, T>::overlap(const S&, const S&, std::vector<long unsigned int>&) const’:
../cpp/IITreeBFS.h:65:7: error: ‘max_level’ was not declared in this scope
   65 |   if (max_level < 0) return false;
      |       ^~~~~~~~~
make: *** [bedcov-iitree-bfs] Error 1

Thank you!