Removed emptiness check from cv::hconcat and cv::vconcat. Sometimes you want to concatenate with an empty matrix.

Conflicts:
	modules/core/test/test_arithm.cpp
	modules/cuda/src/cascadeclassifier.cpp
	modules/imgproc/doc/geometric_transformations.rst
	modules/objdetect/src/hog.cpp
	modules/ocl/perf/perf_imgproc.cpp
	modules/ocl/src/gftt.cpp
	modules/ocl/src/moments.cpp