monitor: refactor error_vprintf()

The monitor_vprintf() code will return -1 if either the monitor
is NULL, or the monitor is QMP. The error_vprintf() code can
take advantage of this to avoid having to duplicate the same
checks, and instead simply look at the return value.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

monitor/monitor.c

@@ -269,16 +269,21 @@ void monitor_printc(Monitor *mon, int c)
 }
 
 /*
- * Print to current monitor if we have one, else to stderr.
+ * Print to the current human monitor if we have one, else to stderr.
  */
 int error_vprintf(const char *fmt, va_list ap)
 {
     Monitor *cur_mon = monitor_cur();
-
-    if (cur_mon && !monitor_cur_is_qmp()) {
-        return monitor_vprintf(cur_mon, fmt, ap);
+    /*
+     * This will return -1 if 'cur_mon' is NULL, or is QMP.
+     * IOW this will only print if in HMP, otherwise we
+     * fallback to stderr for QMP / no-monitor scenarios.
+     */
+    int ret = monitor_vprintf(cur_mon, fmt, ap);
+    if (ret == -1) {
+        ret = vfprintf(stderr, fmt, ap);
     }
-    return vfprintf(stderr, fmt, ap);
+    return ret;
 }
 
 static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {