efi: payload: gracefully handle NULL parent image device path

device_path_to_filepath may be called on a device pth that contains no
file path. In that case, the function should return NULL instead of
dereferencing the NULL pointer. Fix this.

Fixes: f1230c7 ("efi: payload: dynamically determine bootloader file name")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20240611065718.2899625-3-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Author: a3f

efi/devicepath.c

@@ -824,6 +824,9 @@ char *device_path_to_filepath(const struct efi_device_path *dev_path)
 		dev_path = next_device_path_node(&fp->header);
 	}
 
+	if (!fp)
+		return NULL;
+
 	path = strdup_wchar_to_char(fp->path_name);
 	if (!path)
 		return NULL;