efi_loader: loaded images cannot be started twice

If an image already has been started, return EFI_INVALID_PARAMETER when
StartImage() is called for the same handle again.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index 251dfc4..275850a 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -2863,6 +2863,9 @@
 	EFI_ENTRY("%p, %p, %p", image_handle, exit_data_size, exit_data);
 
 	/* Check parameters */
+	if (image_obj->header.type != EFI_OBJECT_TYPE_LOADED_IMAGE)
+		return EFI_EXIT(EFI_INVALID_PARAMETER);
+
 	ret = EFI_CALL(efi_open_protocol(image_handle, &efi_guid_loaded_image,
 					 &info, NULL, NULL,
 					 EFI_OPEN_PROTOCOL_GET_PROTOCOL));