ovsdb-data: Fix overflow in ovsdb_datum_sort_unique()'s return value. #6607

Job	Run time
dpdk gcc (ubuntu-24.04)	8s
osx clang --disable-ssl	2m 7s
libreswan (ubuntu-24.04)	5s
build oss-fuzz fuzzers	2m 54s
linux deb no dpdk	5m 6s
linux rpm fedora	4m 16s
clang-analyze	20m 38s
linux gcc --disable-ssl	2m 55s
linux clang --disable-ssl	2m 37s
linux gcc c99	2m 53s
linux clang c99	2m 51s
linux gcc test	8m 26s
linux clang address,undefined test	16m 36s
linux gcc test --enable-shared	11m 46s
linux clang test --enable-shared	11m 12s
linux gcc check check-dpdk dpdk	19m 6s
linux clang check check-dpdk dpdk	18m 37s
linux gcc test -ljemalloc	9m 19s
linux clang test -ljemalloc	9m 3s
linux gcc --enable-afxdp	2m 47s
linux clang --enable-afxdp	2m 43s
linux gcc dpdk --enable-shared	3m 50s
linux clang dpdk --enable-shared	3m 59s
linux gcc dpdk-shared	3m 16s
linux clang dpdk-shared	3m 7s
linux gcc dpdk-shared --enable-shared	3m 57s
linux clang dpdk-shared --enable-shared	3m 49s
linux gcc m32 --disable-ssl	2m 35s
linux gcc check-ovsdb-cluster	7m 1s
linux gcc check-kernel -100	10m 52s
linux gcc check-kernel 100-	17m 23s
linux clang address,undefined check-kernel -100	13m 54s
linux clang address,undefined check-kernel 100-	18m 34s
linux gcc check-offloads -100	10m 2s
linux gcc check-offloads 100-	11m 42s
linux gcc dpdk check-system-userspace	12m 33s
linux clang address,undefined dpdk check-system-userspace	15m 58s
linux gcc dpdk check-system-tso	12m 18s
linux gcc dpdk check-afxdp	12m 6s
	5h 23m 1s

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