Fixed assertion issue when refresh_token is not used and access_token is expired.

Author: pszalko

Sources/OAuth2Client/NXOAuth2Connection.m

@@ -169,7 +169,7 @@ - (NSURLConnection *)createConnection;
         // if token is expired don't bother starting this connection.
         NSDate *tenSecondsAgo = [NSDate dateWithTimeIntervalSinceNow:(-10)];
         NSDate *tokenExpiresAt = client.accessToken.expiresAt;
-        if ([tenSecondsAgo earlierDate:tokenExpiresAt] == tokenExpiresAt) {
+        if (nil != client.accessToken.refreshToken && [tenSecondsAgo earlierDate:tokenExpiresAt] == tokenExpiresAt) {
             [self cancel];
             [client refreshAccessTokenAndRetryConnection:self];
             return nil;