Whenever the SPF computation determined that there is more than one primary next-hop for a prefix, it does not program any LFA next-hop in RTM. In this case, the LDP FEC resolves to the multiple primary next-hops, which provides the required protection.
Also, when the system ECMP value is set to ecmp=1 or to no ecmp, which translates to the same and is the default value, SPF can use the overflow ECMP links as LFA next-hops in these two cases.