Fix reads on the group key management cluster to handle chunking corr… #5516

Job	Run time
Build framework (macos-release-availability, -sdk macosx -configuration Release OTHER_CFLAGS='$...	11m 14s
Run framework tests (asan, -enableAddressSanitizer YES -enableUndefinedBehaviorSanitizer YES)	2m 50s
Build framework (ios-release, -sdk iphoneos -configuration Release OTHER_CFLAGS='${inherited} -We...	14m 6s
Build TV Casting Bridge example	3m 54s
Run framework tests (asan-global-storage, -enableAddressSanitizer YES -enableUndefinedBehaviorSan...	1m 15s
Build framework (ios-debug, -sdk iphoneos -configuration Debug OTHER_CFLAGS='${inherited} -Werr...	17m 17s
Run framework tests (tsan, -enableThreadSanitizer YES)	1m 15s
Build framework (tvos-debug, -sdk appletvos -configuration Debug OTHER_CFLAGS='${inherited} -Wer...	10m 58s
Build framework (watchos-debug, -sdk watchos -configuration Debug OTHER_CFLAGS='${inherited} -...	3m 36s
Build Darwin	0s
	1h 6m 25s

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