Fix wrong behavior of the revised text widget when moving the cursor … #3405

Job	Run time
test (gcc)	4m 9s
build (gcc)	1m 54s
test (gcc, --disable-xft)	4m 12s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 45s
test (gcc, --enable-symbols)	3m 37s
build (gcc, --disable-shared)	1m 42s
build (gcc, --disable-xft)	1m 47s
build (gcc, --disable-xss)	2m 14s
build (gcc, --enable-symbols)	1m 15s
build (clang)	2m 2s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 54s
build (clang, --disable-shared)	1m 57s
build (clang, --disable-xft)	1m 55s
build (clang, --disable-xss)	1m 54s
build (clang, --enable-symbols)	1m 30s
	33m 47s

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