Refactor: check if place holders in custom tms url contains any space within

[Sujanadh]

Updates:

• used pattern r"\{\s*[xyz]+\s*\}" to check if the place holders contains any space within
• returns True if matches which aborts the background task to generate tiles with invalid tms
• if no placeholders in url, the result will be False. So, pattern will search for spaces only if placeholders {z}/{x}/{y} are in url.