C and C++ still haven't fixed this egregarious bug in the standard.
There is no reason for single line, un-braced blocks. People use them to show off how "cool" they are that they don't need to brace because it's only one line.
It makes for difficult to spot bugs like this. We need to actually yell at the people on the standards committees to FIX THE BUGS in the standard. There are other really obvious ones and they all should be fixed before adding more new features. YES I'M LOOKING AT YOU C++14!
There are plenty of ways you can make a new standard still work alongside code from an old one (compile old, broke, brittle, stupid code with a compiler flag indicating the old standard and new, beter files (yes "translation units c++") with the new one. Introduce a #THIS_FILE_IS_STUPID pragma to disable sanity on old code compiled with the new standard and plenty of others. Pick one, bless, it, implement it and FIX THIS CRAP
The 35th and 36th incidences of the words "goto fail;" in that file are the problem, not easy to spot until you look really closely and it's a bug that a sane standard would make impossible. FIX IT!!