hmp: Simplify how qmp_human_monitor_command() gets output

Commit 48c043d "hmp: human-monitor-command: stop using the Memory
chardev driver" left us "if string is non-empty, duplicate it, else
duplicate the empty string".  Meh.  Duplicate it unconditionally.

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201211171152.146877-2-armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

monitor/misc.c

@@ -136,11 +136,7 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
     handle_hmp_command(&hmp, command_line);
 
     WITH_QEMU_LOCK_GUARD(&hmp.common.mon_lock) {
-        if (qstring_get_length(hmp.common.outbuf) > 0) {
-            output = g_strdup(qstring_get_str(hmp.common.outbuf));
-        } else {
-            output = g_strdup("");
-        }
+        output = g_strdup(qstring_get_str(hmp.common.outbuf));
     }
 
 out: