missing frame on MacOSX clang-compiled app

DrM says:

```
~~Dr.M~~ Error #1: UNADDRESSABLE ACCESS beyond heap bounds: reading 0x00a08e68-0x00a08e69 1 byte(s)
~~Dr.M~~ # 0 libc++.1.dylib!std::__1::basic_string<>::compare
~~Dr.M~~ # 1 libc++.1.dylib!std::__1::basic_string<>::compare
~~Dr.M~~ # 2 parse_page [/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:3799]
~~Dr.M~~ # 3 main [/Users/.../main.cpp:533]
```

lldb says:

```
frame #10: 0x9b1d35a0 libc++.1.dylib`std::__1::basic_string, std::__1::allocator >::compare(char const*) const + 54
frame #11: 0x000f5611 a.out`parse_page(int, std::__1::basic_string, std::__1::allocator > const&, std::__1::basic_ostream >&) [inlined] bool std::__1::operator==, std::__1::allocator >(__lhs=0x00a08e68, __rhs="Q") + 24 at string:3799
frame #12: 0x000f55f9 a.out`parse_page(num=25, round="FINAL", ostr=0xbff15580) + 16553 at main.cpp:445
frame #13: 0x000f8724 a.out`main(argc=2, argv=0xbff15918) + 5828 at main.cpp:533
frame #14: 0x911816ad libdyld.dylib`start + 1
```

The app is built -O0. I have some logs and may be able to analyze why it skipped.