fix pre-allocation when changing priority #3166

Job	Run time
clang-tidy	9m 50s
build (asio-debugging=on picker-debugging=on)	6m 56s
check headers	4m 0s
build (extensions=off logging=off streaming=off super-seeding=off share-mode=off predictive-piece...	4m 42s
build dist (ubuntu-20.04)	2m 40s
build (crypto=gcrypt)	5m 8s
Fuzzers	8m 31s
build dist (ubuntu-22.04)	2m 24s
pre-commit	14s
build (mmap-disk-io=off)	6m 3s
Simulations	9m 2s
Tests (address-sanitizer=norecover undefined-sanitizer=norecover crypto=openssl)	5m 15s
Tests (toolset=clang logging=off address-sanitizer=norecover undefined-sanitizer=norecover)	11m 21s
Tests (thread-sanitizer=norecover crypto=openssl release debug-symbols=on cxxflags=-Wno-tsan)	6m 32s
Tests (crypto=gnutls)	6m 39s
Tests (deprecated-functions=off)	4m 28s
	1h 33m 45s

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