bpo-37702: Fix SSL's certificate-store leak on Windows (GH-15632)

ssl_collect_certificates function in _ssl.c has a memory leak. Calling CertOpenStore() and CertAddStoreToCollection(), a store's refcnt gets incremented by 2. But CertCloseStore() is called only once and the refcnt leaves 1. (cherry picked from commit ed70129) Co-authored-by: neonene <53406459+neonene@users.noreply.github.com>

Author: miss-islington

Misc/NEWS.d/next/Windows/2019-07-29-16-49-31.bpo-37702.Lj2f5e.rst

@@ -0,0 +1,2 @@
+Fix memory leak on Windows in creating an SSLContext object or
+running urllib.request.urlopen('https://...').

Modules/_ssl.c

@@ -5448,6 +5448,7 @@ ssl_collect_certificates(const char *store_name)
  if (result) {
  ++storesAdded;
  }
+ CertCloseStore(hSystemStore, 0); /* flag must be 0 */
  }
  }
  if (storesAdded == 0) {