hw/display/qxl: Have qxl_log_command Return early if no log_cmd handler

Only 3 command types are logged: no need to call qxl_phys2virt()
for the other types. Using different cases will help to pass
different structure sizes to qxl_phys2virt() in a pair of commits.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20221128202741.4945-2-philmd@linaro.org>

hw/display/qxl-logger.c

@@ -247,6 +247,16 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
             qxl_name(qxl_type, ext->cmd.type),
             compat ? "(compat)" : "");
 
+    switch (ext->cmd.type) {
+    case QXL_CMD_DRAW:
+        break;
+    case QXL_CMD_SURFACE:
+        break;
+    case QXL_CMD_CURSOR:
+        break;
+    default:
+        goto out;
+    }
     data = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
     if (!data) {
         return 1;
@@ -269,6 +279,7 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
         qxl_log_cmd_cursor(qxl, data, ext->group_id);
         break;
     }
+out:
     fprintf(stderr, "\n");
     return 0;
 }