fix pre-allocation when changing priority #3171

Job	Run time
build (asio-debugging=on picker-debugging=on)	6m 56s
check headers	4m 2s
build (extensions=off logging=off streaming=off super-seeding=off share-mode=off predictive-piece...	4m 53s
clang-tidy	10m 45s
build (crypto=gcrypt)	5m 12s
build dist (ubuntu-20.04)	3m 12s
build (mmap-disk-io=off)	7m 11s
build dist (ubuntu-22.04)	2m 53s
Fuzzers	8m 40s
pre-commit	14s
Simulations	8m 26s
Tests (address-sanitizer=norecover undefined-sanitizer=norecover crypto=openssl)	5m 45s
Tests (toolset=clang logging=off address-sanitizer=norecover undefined-sanitizer=norecover)	12m 40s
Tests (thread-sanitizer=norecover crypto=openssl release debug-symbols=on cxxflags=-Wno-tsan)	5m 32s
Tests (crypto=gnutls)	4m 50s
Tests (deprecated-functions=off)	5m 17s
	1h 36m 28s

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