highgui module: mouse wheel - modification keys fixed, wheel event value is CV_EVENT_MOUSEWHEEL or CV_EVENT_MOUSEHWHEEL

  * resolve #5183

highgui module: using event->scroll.delta_{x,y} instead parsing direction and added widget event mask GDK_SMOOTH_SCROLL_MASK for GTK>=3.4

highgui: window_gtk.cpp directive boolean operations or/and replaced by ||/&& to keep compatible with older systems

AutoBuffer::allocate(nsz) didn't work properly when
(sz < nsz < fixed_size). In this case sz remained unchanged.

# Resolved Conflicts:
#	modules/videoio/include/opencv2/videoio.hpp

CMake doesn't work with empty paths ("") or paths which contains "./"

change the `while` loop to check if the two windows created by this example still exist, stop the program otherwise