dell: catch invalid dock component requests
dell: catch invalid dock component requests

Test if g_strrstr returns NULL, as this means the string was
modified and other requests predicated on this will fail miserably.

hughsie/fwupd,superm1/fwupd,superm1/fwupd,hughsie/fwupd,vathpela/fwupd,vathpela/fwupd,vathpela/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,superm1/fwupd,vathpela/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd