Assign ISA=NA for non-allocated participants

[PeterJacko]

In lAllocIntr.R, if all(alloc_ratio == 0), nothing is done to newdat_df, but in the else statement, column ISA is created. We should also create the ISA column using lPltfTrial$lSnap$newdat_df$ISA and perhaps assign NA to all of them.

This is because the subsequent code in lFnDef.R, assumes the existence of column ISA, in:
for (i in unique(lPltfTrial$lSnap$newdat_df$ISA)) {
lPltfTrial$isa[[i]]$tempPats <-
subset(lPltfTrial$lSnap$newdat_df, ISA == i)
}

It would be useful if the datasets always had the same structure regardless of what happens.