[outofcore] Fix compile issue due to missing include under MSVC 2019

[SunBlack]

Without this include I get (MSVC 16.9.4):

1>C:\dev\pcl\outofcore\include\pcl/outofcore/outofcore_breadth_first_iterator.h(103,19): error C2143: syntax error: missing ';' before '<'
1>C:\dev\pcl\outofcore\include\pcl/outofcore/outofcore_breadth_first_iterator.h(105): message : see reference to class template instantiation 'pcl::outofcore::OutofcoreBreadthFirstIterator<PointT,ContainerT>' being compiled
1>C:\dev\pcl\outofcore\include\pcl/outofcore/outofcore_breadth_first_iterator.h(103,1): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>C:\dev\pcl\outofcore\include\pcl/outofcore/outofcore_breadth_first_iterator.h(103,1): error C2238: unexpected token(s) preceding ';'

[mvieth]

Thanks!