x86/boot: don't blindly mark VGA in graphics mode on MB2 path

Setting ->orig_video_isVGA to the specific marker should be done only when
the VBE tag is present and the FRAMEBUFFER is either absent or indicates
RGB type. Since the "video" variable now starts out non-NULL, this
property was broken when in particular neither of the tags are present. To
move back to at least close to original behavior, add a 2nd check to said
conditional.

Fixes: d5a73cdc6b ("x86/boot: Use boot_vid_info variable directly from C code")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
master commit: c7b7429854
master date: 2026-06-25 13:37:33 +0200

xen/arch/x86/boot/reloc.c

@@ -339,7 +339,7 @@ static multiboot_info_t *mbi2_reloc(uint32_t mbi_in, memctx *ctx)
  end:
 
 #ifdef CONFIG_VIDEO
-    if ( video )
+    if ( video && video->lfb_size )
         video->orig_video_isVGA = 0x23;
 #endif