scripts: don't fail if there is no diff to commit

scripts/update_c_library.sh

@@ -74,7 +74,7 @@ echo -e "\0033[34mFinished generating c headers\0033[0m\n"
 cd $CLIBRARY_PATH
 git add --all :/ || exit 1
 COMMIT_MESSAGE="autogenerated headers for rev https://github.com/mavlink/mavlink/tree/"$MAVLINK_GITHASH
-git commit -m "$COMMIT_MESSAGE" || exit 1
+git commit -m "$COMMIT_MESSAGE" || exit 0  # for the case when nothing is there to commit
 
 # push to c_library repository
 git push $CLIBRARY_GIT_REMOTENAME $CLIBRARY_GIT_BRANCHNAME || exit 1