WIP: Fix BLOCKSTRETCHACTION object #4649

Job	Run time
linux-cmake	2m 35s
linux (CFLAGS="-O1 -fno-omit-frame-pointer -fsanitize=address -fno-var-tracking" --disable-bindin...	3m 25s
linux (CC="clang")	4m 2s
mingw	23m 34s
macOS	5m 35s
linux (--enable-release)	23m 45s
mips32-big-endian	14m 32s
linux (--enable-gcov --disable-bindings --disable-docs CFLAGS="-O0 -g")	4m 37s
ppc64-big-endian	8m 15s
linux (--disable-write --disable-docs)	4m 35s
vs2019	4m 58s
vs2019-ninja	4m 16s
linux (CFLAGS="-O2 -m32" --disable-bindings --disable-docs)	3m 46s
linux (CFLAGS="-O2 -fno-omit-frame-pointer -fsanitize=undefined -fno-var-tracking" --disable-bind...	11m 38s
mingw-cmake	3m 25s
	2h 2m 58s

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