Added error checking for samples.

docs/examples/smtp-tls.c

@@ -139,6 +139,10 @@ int main(void)
 
     /* send the message (including headers) */
     res = curl_easy_perform(curl);
+    /* Check for errors */
+    if(res != CURLE_OK)
+      fprintf(stderr, "curl_easy_perform() failed: %s\n",
+              curl_easy_strerror(res));
 
     /* free the list of recipients and clean up */
     curl_slist_free_all(recipients);