[Bug libstdc++/97415] Invalid pointer comparison in stringbuf::str() (reported by pointer-compare AddressSanitizer)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97415

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk so far. I'm undecided whether it needs to be backported.
Although the comparison with null is formally unspecified, I think all the
compilers we support behave as expected.