[common] rect: fix avx unaligned bytes copy #2531

Job	Run time
host-linux	35s
client (gcc, g++, xdg-shell, Release)	1m 3s
docs	54s
client (gcc, g++, xdg-shell, Debug)	58s
client (gcc, g++, libdecor, Release)	1m 4s
host-windows-cross	1m 0s
client (gcc, g++, libdecor, Debug)	43s
host-windows-native	1m 32s
client (clang, clang++, xdg-shell, Release)	1m 24s
module	16s
client (clang, clang++, xdg-shell, Debug)	1m 16s
obs (gcc)	41s
client (clang, clang++, libdecor, Release)	1m 17s
obs (clang)	34s
client (clang, clang++, libdecor, Debug)	1m 13s
	14m 30s

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