ovsdb-idl: Fix use of uninitialized datum for graph consistency check. #2541

Job	Run time
osx clang --disable-ssl	1m 25s
linux rpm fedora	4m 25s
dpdk gcc (ubuntu-24.04)	2m 49s
linux deb no dpdk	4m 56s
linux gcc --disable-ssl	2m 52s
linux clang --disable-ssl	2m 13s
linux gcc c99	2m 21s
linux clang c99	2m 12s
linux gcc test	7m 28s
linux clang test asan	13m 41s
linux clang test ubsan	9m 15s
linux gcc test --enable-shared	10m 26s
linux clang test --enable-shared	10m 23s
linux gcc test dpdk	8m 7s
linux clang test dpdk	7m 50s
linux gcc test -ljemalloc	8m 4s
linux clang test -ljemalloc	8m 33s
linux gcc --enable-afxdp	2m 15s
linux clang --enable-afxdp	4m 9s
linux gcc dpdk --enable-shared	3m 35s
linux clang dpdk --enable-shared	2m 54s
linux gcc dpdk-shared	3m 35s
linux clang dpdk-shared	3m 34s
linux gcc dpdk-shared --enable-shared	3m 38s
linux clang dpdk-shared --enable-shared	2m 58s
linux gcc m32 --disable-ssl	3m 13s
	2h 16m 51s

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