ofPixels memory allocation size fix #1202

Job	Run time
build-msys2 (mingw64)	12m 17s
build-msys2 (ucrt64)	12m 9s
build-ios-tvos (ios, macos)	1m 41s
build-msys2 (clang64)	8m 2s
build-linux64 (linux64, 64gcc6)	4m 5s
build-ios-tvos (tvos, macos)	2m 59s
build-emscripten (emscripten)	3m 5s
build-macos (osx, xcode)	1m 9s
build-vs2022 (x64)	10m 9s
rpi-build (armv6l, armhf, arm-linux-gnueabihf, 1)	1m 55s
build-macos (osx, makefiles)	1m 28s
build-vs2022 (ARM64)	12m 44s
rpi-build (armv7l, armhf, arm-linux-gnueabihf, 1)	2m 0s
build-vs2022 (ARM64EC)	11m 18s
rpi-build (aarch64, arm64, aarch64-linux-gnu, 1)	2m 12s
	1h 27m 13s

Provide feedback