Control flow fix in femtoscopy lines

Fixes the control flow of some of the ift femtoscopy lines. The final algorithm in the line was not the final algorithm in the control flow which doesn't make sense for the flow. For example: old version: [xi_pairs, xis], new version: [xis, xi_pairs], where xis is the input to xi_pairs so it always has to run before xi_pairs even though xis is behind it in the old control flow. This might make the line slightly faster but nothing major.