py-version.sh: Make it work in case no git tag is present.
diff --git a/py/py-version.sh b/py/py-version.sh
index 42474ef..daa2548 100755
--- a/py/py-version.sh
+++ b/py/py-version.sh
@@ -1,6 +1,7 @@
#!/bin/bash
-git_tag="$(git describe --dirty || echo unknown)"
+# Note: git describe doesn't work if no tag is available
+git_tag="$(git describe --dirty 2> /dev/null || git rev-parse --short HEAD)"
git_hash="$(git rev-parse --short HEAD 2> /dev/null || echo unknown)"
git_files_are_clean=1
# Check if there are any modified files.