64ddca513df9cac80ceb4e1f45777a22b10a44c3 dynSeries: making possible to concatanate empty series; fixing bugs

================================ DYNARE MAKE CHECK MATLAB RESULTS ================================ | TOTAL: 194 | PASS: 193 | FAIL: 0 | XFAIL: 1 | XPASS: 0

================================ DYNARE MAKE CHECK OCTAVE RESULTS ================================ | TOTAL: 192 | PASS: 191 | FAIL: 0 | XFAIL: 1 | XPASS: 0

A full log can be found on karaba in '/tmp/dynare-master-check-AnmTERrPAa.log'.