Accessing the file size returns -1 on error, for file packing this
was passed directly to an allocation which would wrap around to
SIZE_T_MAX and fail to allocate. In other cases zero was treated
as an error value but -1 wasn't.
Add checks for the error return value, also warn that packing files over
2gb isn't supported.
Also see #103343.
Couldn't move two files yet:
* `softbody.c`: The corresponding regression test fails. It seems like the
conversion to C++ changes floating point accuracy, but it's not clear where that happens exactly.
* `writeffmpeg.c`: Is a bit more complex to convert because of the static array in `av_err2str`.
Pull Request: https://projects.blender.org/blender/blender/pulls/110182
