Avoid “stoi: no conversion” when Windows newlines are present

[paulmelnikow]

While different platforms have different conventions for handling newlines, and std::getline only follows the convention of the current platform. Of course OBJ files could be created on one platform and read on another, which leads to problems.

Here's a bit of explanation:

https://stackoverflow.com/questions/6089231/getting-std-ifstream-to-handle-lf-cr-and-crlf

Adapted from the advice there, the fix is to trim the trailing '\r' when it's present.