(cherry-pick): Fix [13ac26b35d]: wm iconbitmap does not correctly set… #506

Job	Run time
build (gcc)	2m 16s
test (gcc)	4m 25s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 38s
test (gcc, --disable-xft)	4m 23s
build (gcc, --disable-xft)	1m 38s
test (gcc, --enable-symbols)	3m 32s
build (gcc, --disable-xss)	1m 43s
build (gcc, --enable-symbols)	1m 15s
build (clang)	1m 49s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 22s
build (clang, --disable-xft)	1m 52s
build (clang, --disable-xss)	2m 0s
build (clang, --enable-symbols)	1m 34s
	30m 27s

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