functions: add dirty fall back to commit id if no version tag can be found

build/functions.bash

@@ -21,8 +21,13 @@ function build_git_repo()
 		VERSION=$(newest_git_tag)
 	fi
 	
-	git verify-tag "$VERSION"
-	git checkout "$VERSION"
+	if [ -n "$VERSION" ] ; then
+		git verify-tag "$VERSION"
+		git checkout "$VERSION"
+	else
+		LAST_COMMIT_ID=$(git log --pretty="format:%h" -n1)
+		VERSION="0.1+git$LAST_COMMIT_ID"
+	fi
 	mv ../debian/ .
 	VERSION_CHANGELOG=$( echo $VERSION | sed -e 's/v//g')
 	sed -e "s/NAME_PLACEHOLDER/$NAME/g" -i ./debian/changelog