Issue #29142: Fix suffixes in no_proxy handling in urllib.

In urllib.request, suffixes in no_proxy environment variable with
leading dots could match related hostnames again (e.g. .b.c matches a.b.c).
Patch by Milan Oberkirch.

Lib/urllib/request.py

@@ -2450,6 +2450,7 @@ def proxy_bypass_environment(host, proxies=None):
     no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]
     for name in no_proxy_list:
         if name:
+            name = name.lstrip('.')  # ignore leading dots
             name = re.escape(name)
             pattern = r'(.+\.)?%s$' % name
             if (re.match(pattern, hostonly, re.I)