FTDet: hack to cope for JIRATICKET-LHCBUCNDB-68

implement small hack to cope for some change/inconsistency in the DDDB description of the sipms and modules gaps (namely, the V5 fibreMat X size does not account anymore for the fact that the inter-module (ie single real fibremat (4 sipms)) gap is in front of and has a smaller size (0.2mm) than the sipm gaps and so has not to be counted as addtional dead zone (and those gaps are in addition rejected at the end of the 4-module fibremat (16 sipms)). Remember that the sipm gaps are simulated in FTDet and not in the DDDB, whereas the inter-module gaps (0.2mm) are in the DDDB.). The simple solution to recover the active/dead area ratio is to slightly change in FTDet the size of the sipm gap (but even with this a (small) part of the efficiency loss is displaced from the sipms to the modules (16 sipms) edges. The sipm gap goes from 0.225mm to 0.175mm, and 320.225 = 320.175 + 20.8 =7.2mm of dead area per module (16 sipms, 0.8mm = 40.2mm of inter single fibremat (4 sipms) gap)