curl: improved cleanup in upload error path

Memory leak found by torture test 58

Closes #4705

src/tool_operhlp.c

@@ -115,16 +115,17 @@ char *add_file_name_to_url(char *url, const char *filename)
         urlbuffer = aprintf("%s/%s", url, encfile);
 
       curl_free(encfile);
+
+      if(!urlbuffer) {
+        url = NULL;
+        goto end;
+      }
+
       Curl_safefree(url);
-
-      if(!urlbuffer)
-        return NULL;
-
       url = urlbuffer; /* use our new URL instead! */
     }
-    else
-      Curl_safefree(url);
   }
+  end:
   curl_easy_cleanup(curl);
   return url;
 }