cppzmq fails to install if libzmq is not avaible as as static library

[ffontaine]

When trying to update cppzmq in buildroot, I found that if libzmq is only available as a shared library and not a static one then cmake fails with:

-- CMake libzmq package not found, trying again with pkg-config (normal install of zeromq)
-- Found PkgConfig: /home/fabrice/buildroot/output/host/bin/pkg-config (found version "0.28") 
CMake Error at CMakeLists.txt:20 (message):
  ZeroMQ was not found, neither as a CMake package nor via pkg-config

This is due to the fact that ZeroMQ_FOUND is not set to ON even if ZEROMQ_LIBRARY is TRUE:

if(ZeroMQ_LIBRARY AND ZeroMQ_STATIC_LIBRARY)
    set(ZeroMQ_FOUND ON)
endif()

Could you explain me why these lines were added to cppzmq/libzmq-pkg-config/FindZeroMQ.cmake?

[sigiesec]

Looks for me like this should be OR rather than AND. Can you try this and maybe send a PR with the change?