Tweak Avatar::Private::get() #1448

Job	Run time
CI (ubuntu-22.04, 6.4, e2ee)	1m 11s
CI (ubuntu-22.04, 6.4)	1m 37s
CI (ubuntu-22.04, 6.4, GCC, e2ee)	1m 5s
CI (ubuntu-22.04, 6.4, GCC)	55s
CI (ubuntu-22.04, 5.15, e2ee)	1m 36s
CI (macos-11, 6.4, e2ee)	8m 0s
CI (macos-11, 6.4)	6m 35s
CI (macos-11, 5.15, e2ee)	7m 4s
CI (windows-2019, 6.4, e2ee)	1m 42s
CI (windows-2019, 6.4)	2m 0s
CI (windows-2019, 5.15, e2ee)	2m 4s
CI (ubuntu-22.04, 5.15, e2ee, update-api, codeql)	1m 24s
CI (ubuntu-22.04, 5.15, GCC, update-api)	1m 36s
	36m 49s

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