py-version.sh: Make it work in case no git tag is present.

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.