(cherry-pick): Fix [13ac26b35d]: wm iconbitmap does not correctly set… #1502

Job	Run time
build (gcc)	1m 41s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 42s
build (gcc, --disable-xft)	1m 39s
build (gcc, --disable-xss)	1m 39s
test (gcc)	4m 4s
build (gcc, --enable-symbols)	1m 12s
test (gcc, --disable-xft)	4m 15s
build (clang)	1m 50s
test (gcc, --enable-symbols)	3m 31s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 1s
build (clang, --disable-xft)	1m 52s
build (clang, --disable-xss)	1m 50s
build (clang, --enable-symbols)	1m 24s
	28m 40s

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