[Backport 2.x] Avoid showing unhelpful error toast when datasource is not yet selected

[opensearch-trigger-bot]

Backport e4fdd25 from #1186.

[opensearch-trigger-bot]

The backport to 2.17 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security-analytics-dashboards-plugin/backport-2.17 2.17
# Navigate to the new working tree
pushd ../.worktrees/security-analytics-dashboards-plugin/backport-2.17
# Create a new branch
git switch --create backport-1187-to-2.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 f690f93c5b070f5d03c2b054006ca958a4e66e26
# Push it to GitHub
git push --set-upstream origin backport-1187-to-2.17
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics-dashboards-plugin/backport-2.17

Then, create a pull request where the base branch is 2.17 and the compare/head branch is backport-1187-to-2.17.