gam-install.sh: check curl response code

src/gam-install.sh

@@ -120,14 +120,24 @@ else
   curl_opts=( "$GHCLIENT" )
 fi
 echo_yellow "Checking GitHub URL $release_url for $gamversion GAM release ($check_type)..."
-release_json=$(curl \
+release_response=$(curl \
 	--silent \
 	"${curl_opts[@]}" \
 	-H "Accept: application/vnd.github+json" \
 	-H "X-GitHub-Api-Version: 2022-11-28" \
 	"$release_url" \
+        -w "%{http_code}" \
 	2>&1 /dev/null)
 
+response_status="${release_response: -3}"
+release_json="${release_response:0:-4}"
+if [ "$response_status" != "200" ]; then
+  echo_red "ERROR when retrieving ${release_url}:\n\n${release_json}"
+  exit
+else
+  echo_green "done"
+fi
+
 echo_yellow "Getting file and download URL..."
 # Python is sadly the nearest to universal way to safely handle JSON with Bash
 # At least this code should be compatible with just about any Python version ever