Various fixes for ViSP Canny implementation #2218

Job	Run time
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 98)	8m 46s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 11)	25m 41s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-9, /usr/bin/g++-9, 17)	30m 23s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 98)	14m 40s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 11)	23m 10s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/gcc-10, /usr/bin/g++-10, 17)	27m 26s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 98)	9m 25s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 11)	38m 50s
build-ubuntu-dep-apt (ubuntu-20.04, /usr/bin/clang, /usr/bin/clang++, 17)	33m 25s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-9, /usr/bin/g++-9, 98)	6m 53s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-9, /usr/bin/g++-9, 11)	21m 21s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-9, /usr/bin/g++-9, 17)	33m 26s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-10, /usr/bin/g++-10, 98)	7m 33s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-10, /usr/bin/g++-10, 11)	23m 5s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/gcc-10, /usr/bin/g++-10, 17)	27m 58s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/clang, /usr/bin/clang++, 98)	9m 30s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/clang, /usr/bin/clang++, 11)	31m 9s
build-ubuntu-dep-apt (ubuntu-latest, /usr/bin/clang, /usr/bin/clang++, 17)	36m 12s
	6h 48m 53s

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