Fix [3981091e] Segmentation fault with bogus resource value (X11) #1453

Job	Run time
build (gcc)	1m 39s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 35s
test (gcc)	3m 54s
build (gcc, --disable-xft)	1m 38s
test (gcc, --disable-xft)	4m 11s
build (gcc, --disable-xss)	1m 36s
test (gcc, --enable-symbols)	3m 28s
build (gcc, --enable-symbols)	1m 11s
build (clang)	2m 12s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 51s
build (clang, --disable-xft)	1m 50s
build (clang, --disable-xss)	1m 51s
build (clang, --enable-symbols)	1m 25s
	28m 21s

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