Avoid uninitialized memory assignment in TRTToTCondAlg
The last remaining issue in ATLASRECS-5068 is a Valgrind complaint, most likely an uninitialized memory allocation, that is hopefully fixed by this MR. It just refrains to add a vector to a map of vectors, if the vector size is zero. I tried to run Valgrind various ways and in the output I found no mention of TRTToTCondAlg.