ui/console: Fix console resize with placeholder surface

In `qemu_console_resize()`, the old surface of the console is keeped if the new
console size is the same as the old one. If the old surface is a placeholder,
and the new size of console is the same as the placeholder surface (640*480),
the surface won't be replace.
In this situation, the surface's `QEMU_PLACEHOLDER_FLAG` flag is still set, so
the console won't be displayed in SDL display mode.
This patch fixes this problem by forcing a new surface if the old one is a
placeholder.

Signed-off-by: Tianlan Zhou <bobby825@126.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20240207172024.8-1-bobby825@126.com>

ui/console.c

@@ -1577,7 +1577,7 @@ void qemu_console_resize(QemuConsole *s, int width, int height)
     assert(QEMU_IS_GRAPHIC_CONSOLE(s));
 
     if ((s->scanout.kind != SCANOUT_SURFACE ||
-         (surface && surface->flags & QEMU_ALLOCATED_FLAG)) &&
+         (surface && !is_buffer_shared(surface) && !is_placeholder(surface))) &&
         qemu_console_get_width(s, -1) == width &&
         qemu_console_get_height(s, -1) == height) {
         return;