Fix nightly version lookup when no nightly tags

Author: cursoragent

scripts/install.sh

@@ -107,7 +107,7 @@ get_latest_stable_version() {
 get_latest_nightly_version() {
     local url="https://api.github.com/repos/${GITHUB_REPO}/releases?per_page=20"
     local version
-    version=$(fetch_github_json "$url" | grep '"tag_name"' | grep 'nightly' | head -n 1 | sed -E 's/.*"tag_name": *"v?([^"]+)".*/\1/')
+    version=$(fetch_github_json "$url" | grep '"tag_name"' | grep 'nightly' | head -n 1 | sed -E 's/.*"tag_name": *"v?([^"]+)".*/\1/' || true)
 
     if [[ -z "$version" ]]; then
         error "Failed to fetch latest nightly version from GitHub. Please check your internet connection."