tool: Fixed incorrect return code when setting HTTP request fails

During initialisation SetHTTPrequest() may fail and cURL would return
PARAM_BAD_USE, which is equivalent to CURLE_NOT_BUILT_IN in cURL error
terms.

Instead, return CURLE_FAILED_INIT as we do for other functions that may
fail during initialisation.

src/tool_operate.c

@@ -314,13 +314,13 @@ static int operate_do(struct Configurable *config)
       if(SetHTTPrequest(config,
                         (config->no_body?HTTPREQ_HEAD:HTTPREQ_GET),
                         &config->httpreq)) {
-        res = PARAM_BAD_USE;
+        res = CURLE_FAILED_INIT;
         goto quit_curl;
       }
     }
     else {
       if(SetHTTPrequest(config, HTTPREQ_SIMPLEPOST, &config->httpreq)) {
-        res = PARAM_BAD_USE;
+        res = CURLE_FAILED_INIT;
         goto quit_curl;
       }
     }