fixed the ordering of contour convex hull points

* partially fixed the issue #4539

* fixed warnings and test failures

* fixed integer overflow (issue #14521)

* added comment to force buildbot to re-run

* extended the test for the issue 4539. Check the expected behaviour on the original contour as well

* added comment; fixed typo, renamed another variable for a little better clarity

* added yet another part to the test for issue #4539, where we run convexHull and convexityDetects on the original contour, without any manipulations. the rest of the test stays the same