Fixing jFEX input data decoder crash.

This MR is meant to fix one crash observed and reported in ATR-27054

The problem was that the Trailers where correctly set, however due to a non-expected word at the end, the algorithm tried to decode the next FPGA. That is was impossible since there are just 4 FPGAs..

The solution was to add one checker to know if there is something to decode, check that at least has two Trailers.