cryptnet: Sign-compare warning fix (try 2)

[Andrew Talbot]

Changelog:
    cryptnet: Sign-compare warning fix.

diff --git a/dlls/cryptnet/cryptnet_main.c b/dlls/cryptnet/cryptnet_main.c
index ffd4d64..e39122b 100644
--- a/dlls/cryptnet/cryptnet_main.c
+++ b/dlls/cryptnet/cryptnet_main.c
@@ -1358,10 +1358,12 @@ BOOL WINAPI CertDllVerifyRevocation(DWORD dwEncodingType, DWORD dwRevType,
         for (i = 0; ret && i < cContext; i++)
         {
             DWORD cbUrlArray;
+            LONG last_error;
 
             ret = CryptGetObjectUrl(URL_OID_CERTIFICATE_CRL_DIST_POINT,
              rgpvContext[i], 0, NULL, &cbUrlArray, NULL, NULL, NULL);
-            if (!ret && GetLastError() == CRYPT_E_NOT_FOUND)
+            last_error = GetLastError();
+            if (!ret && last_error == CRYPT_E_NOT_FOUND)
             {
                 error = CRYPT_E_NO_REVOCATION_CHECK;
                 pRevStatus->dwIndex = i;