Return full path if available.

def get_file_fullpath(name, dirname=None):
        # type: (AnyStr, Optional[AnyStr]) -> Optional[AnyStr]
        """Return full path if available."""
        if name is None:
            return None
        if is_string(name):
            name = str(name)
        else:
            raise RuntimeError('The input function name or path must be string!')
        for sep in ['\\', '/', os.sep]:  # Loop all possible separators
            if sep in name:  # name is full path already
                name = os.path.abspath(name)
                return name
        if dirname is not None:
            dirname = os.path.abspath(dirname)
            name = dirname + os.sep + name
        return name