Bail out if web branch is unclean like build does

bump_version

@@ -36,9 +36,19 @@ git submodule update --init --recursive
 
 # configure branch
 pushd MediaBrowser.WebDashboard/jellyfin-web
+
+if ! git diff-index --quiet HEAD --; then
+    popd
+    echo
+    echo "ERROR: Your 'jellyfin-web' submodule working directory is not clean!"
+    echo "This script will overwrite your unstaged and unpushed changes."
+    echo "Please do development on 'jellyfin-web' outside of the submodule."
+    exit 1
+fi
+
 git fetch --all
 git checkout origin/${web_branch} || {
-    echo "jellyfin-web branch ${web_branch} is invalid."
+    echo "ERROR: 'jellyfin-web' branch ${web_branch} is invalid."
     exit 1
 }
 popd