WIP: Fix BLOCKSTRETCHACTION object #4648

Job	Run time
linux-cmake	1m 41s
macOS	5m 25s
linux (CFLAGS="-O1 -fno-omit-frame-pointer -fsanitize=address -fno-var-tracking" --disable-bindin...	3m 20s
linux (CC="clang")	4m 10s
mingw	10m 24s
linux (--enable-release)	10m 36s
mingw-cmake	3m 12s
linux (--enable-gcov --disable-bindings --disable-docs CFLAGS="-O0 -g")	4m 1s
linux (--disable-write --disable-docs)	4m 36s
mips32-big-endian	10m 35s
ppc64-big-endian	8m 26s
linux (CFLAGS="-O2 -m32" --disable-bindings --disable-docs)	3m 38s
vs2019	6m 12s
linux (CFLAGS="-O2 -fno-omit-frame-pointer -fsanitize=undefined -fno-var-tracking" --disable-bind...	10m 34s
vs2019-ninja	4m 52s
	1h 31m 42s

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