Ceph MDS segfault when printing client metrics

Issue

The MDS does segfault when attempting to log client metrics:

#0  0x0000559d7769ee69 in memmove (__len=21, __src=0x7fc5de50ab69, __dest=0x559d7da87fb9) at /usr/include/bits/string_fortified.h:40
#1  boost::container::dtl::memmove_n_source<char const*, unsigned long, char*> (r=0x559d7da87fb9 "", n=21, f=0x7fc5de50ab69 "Unknown metric type: ")
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/detail/copy_move_algo.hpp:211
#2  boost::container::uninitialized_copy_alloc_n_source<boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, char const*, char*> (r=0x559d7da87fb9 "", n=21, f=0x7fc5de50ab69 "Unknown metric type: ")
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/detail/copy_move_algo.hpp:545
#3  boost::container::dtl::insert_range_proxy<boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, char const*, char*>::uninitialized_copy_n_and_update (this=<synthetic pointer>, a=..., n=21, p=0x559d7da87fb9 "")
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/detail/advanced_insert_int.hpp:83
#4  boost::container::vector<char, boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, void>::priv_forward_range_insert_expand_forward<boost::container::dtl::insert_range_proxy<boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, char const*, char*> > (insert_range_proxy=..., n=21, pos=0x559d7da87fb9 "", this=0x559d7af79248)
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/vector.hpp:2964
#5  boost::container::vector<char, boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, void>::priv_forward_range_insert<boost::container::dtl::insert_range_proxy<boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, char const*, char*> > (insert_range_proxy=..., n=21, pos=<optimized out>, this=0x559d7af79248)
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/vector.hpp:2826
#6  boost::container::vector<char, boost::container::small_vector_allocator<char, boost::container::new_allocator<void>, void>, void>::insert<char const*> (
    last=0x7fc5de50ab7e "", first=0x7fc5de50ab69 "Unknown metric type: ", pos=..., this=0x559d7af79248)
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/build/boost/include/boost/container/vector.hpp:1987
#7  StackStringBuf<4096ul>::xsputn (this=0x559d7af79208, s=0x7fc5de50ab69 "Unknown metric type: ", n=21)
    at /usr/src/debug/ceph-16.2.0-152.el8cp.x86_64/src/common/StackStringStream.h:68
#8  0x00007fc5dc0c0da4 in std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, long) () from /lib64/libstdc++.so.6
#9  0x00007fc5de0f0c5e in operator<<(std::ostream&, ClientMetricType const&) () from /usr/lib64/ceph/libceph-common.so.2
#10 0x00007fc5de0f0c69 in operator<<(std::ostream&, ClientMetricType const&) () from /usr/lib64/ceph/libceph-common.so.2
#11 0x00007fc5de0f0c69 in operator<<(std::ostream&, ClientMetricType const&) () from /usr/lib64/ceph/libceph-common.so.2