Non-fatal assertion !(smartlist_len(outdated_dirserver_list) > TOO_MANY_OUTDATED_DIRSERVERS)

A user sent me this email saying that they'd gotten this bug on their relay.

 tor_bug_occurred_(): Bug: ../src/feature/nodelist/microdesc.c:133:
microdesc_note_outdated_dirserver: Non-fatal assertion
!(smartlist_len(outdated_dirserver_list) > TOO_MANY_OUTDATED_DIRSERVERS)
failed. (on Tor 0.4.4.6 )
 Bug: Tor 0.4.4.6: Non-fatal assertion
!(smartlist_len(outdated_dirserver_list) > TOO_MANY_OUTDATED_DIRSERVERS)
failed in microdesc_note_outdated_dirserver at
../src/feature/nodelist/microdesc.c:133. Stack trace: (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(log_backtrace_impl+0x56) [0x55bdb35379d6] (on Tor
0.4.4.6 )
 Bug:     /usr/bin/tor(tor_bug_occurred_+0x16c) [0x55bdb3532bdc] (on Tor
0.4.4.6 )
 Bug:     /usr/bin/tor(microdesc_note_outdated_dirserver+0x147)
[0x55bdb34563c7] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(+0x1085fb) [0x55bdb341d5fb] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(+0x10b588) [0x55bdb3420588] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(connection_dir_reached_eof+0x29) [0x55bdb3422e09]
(on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(connection_handle_read+0x8bc) [0x55bdb33862dc]
(on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(+0x76729) [0x55bdb338b729] (on Tor 0.4.4.6 )
 Bug:     /lib/x86_64-linux-gnu/libevent-2.1.so.6(+0x229ba)
[0x7f0bd5d2e9ba] (on Tor 0.4.4.6 )
 Bug:     /lib/x86_64-linux-gnu/libevent-2.1.so.6(event_base_loop+0x5a7)
[0x7f0bd5d2f537] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(do_main_loop+0xff) [0x55bdb338c9af] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(tor_run_main+0x885) [0x55bdb33793a5] (on Tor
0.4.4.6 )
 Bug:     /usr/bin/tor(tor_main+0x3a) [0x55bdb33772ca] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(main+0x19) [0x55bdb3376e89] (on Tor 0.4.4.6 )
 Bug:     /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xeb)
[0x7f0bd561009b] (on Tor 0.4.4.6 )
 Bug:     /usr/bin/tor(_start+0x2a) [0x55bdb3376eda] (on Tor 0.4.4.6 )