Monitor equalizer with FBO sources leads to crash

[tribal-tec]

Use 3-window.monitor.eqc and change the drawable for the left and/or right segment to FBO:

23755    PipeDraw src/Equalizer/eq/client/gl.cpp:28 1169 Got GL_INVALID_OPERATION after glPopAttrib() in /home/nachbaur/dev/Buildyard/src/Equalizer/eq/client/compositor.cpp:1578

    eq::debugGLError(std::string const&, unsigned int, char const*, int)
    eq::Compositor::resetAssemblyState()
    eq::Channel::resetAssemblyState()
    eq::Channel::frameReadback(lunchbox::uint128_t const&)
    eqPly::Channel::frameReadback(lunchbox::uint128_t const&)
    eq::Channel::_frameReadback(lunchbox::uint128_t const&, std::vector<co::ObjectVersion, std::allocator<co::ObjectVersion> > const&)
    eq::Channel::_cmdFrameReadback(co::ICommand&)
    co::CommandFunc<co::Dispatcher>::operator()(co::ICommand&)
    co::ICommand::operator()()
    co::WorkerThread<eq::CommandQueue>::run()
    eq::detail::RenderThread::run()
    lunchbox::Thread::_runChild()
    lunchbox::Thread::runChild(void*)
    /lib/x86_64-linux-gnu/libpthread.so.0(+0x7f8e) [0x7ffff6fa9f8e]
    /lib/x86_64-linux-gnu/libc.so.6(clone+0x6d) [0x7ffff5914e1d]
23755    PipeDraw src/Equalizer/eq/client/gl.cpp:28 1176 
terminate called after throwing an instance of 'eq::GLException'
  what():   OpenGL Error GL_INVALID_OPERATION

With pbuffer it works though.