fixing seg-fault when wait_for_frames was called before enable_stream
fixing seg-fault when wait_for_frames was called before enable_stream

IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,floe/librealsense,floe/librealsense,IntelRealSense/librealsense,IntelRealSense/librealsense,floe/librealsense,IntelRealSense/librealsense