autogen.sh: Only copy submodules if building from a git branch.
`autogen.sh` fails if building from a standard source tarball. Firstly, git
expects to be called in a git repository, then `copy_submodule_files`
blindly attempts to copy files.
Debian, Ubuntu, Linux Mint, and other derivatives all run `autogen.sh`
before compiling to regenerate build files.
This patch ensures that various git commands are only called and 'dlg' files
are only copied if `autogen.sh` is called from a git repository.
1 file changed
