Linux

allow execution of `on_unknown_torrent` method in the absence of active torrents #2825

Job	Run time
build (asio-debugging=on picker-debugging=on)	24m 12s
build (extensions=off logging=off streaming=off super-seeding=off share-mode=off predictive-piece...	24m 10s
check headers	6m 0s
Fuzzers	11m 13s
build (crypto=gcrypt)	24m 6s
build (mmap-disk-io=off)	24m 10s
pre-commit	59s
clang-tidy	13m 27s
build dist (ubuntu-20.04)	24m 17s
Simulations	24m 12s
build dist (ubuntu-22.04)	24m 8s
Tests (address-sanitizer=norecover undefined-sanitizer=norecover crypto=openssl)	24m 6s
Tests (toolset=clang logging=off address-sanitizer=norecover undefined-sanitizer=norecover)	19m 50s
Tests (thread-sanitizer=norecover crypto=openssl release debug-symbols=on cxxflags=-Wno-tsan)	23m 51s
Tests (crypto=gnutls)	20m 43s
Tests (deprecated-functions=off)	21m 26s
	5h 10m 50s

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