[Bug libstdc++/103853] std::forward_list::merge should check if __list != this

[pavel.kryukov at phystech dot edu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103853

--- Comment #10 from Pavel I. Kryukov <pavel.kryukov at phystech dot edu> ---
Thanks a lot!