[Bug libstdc++/118035] deque bug when inserting an empty iterator interval

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118035

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The fix will be to just return early if inserting no elements, but I'll check
for other problems too.