[12gevmoller_sim] [JeffersonLab/remoll] bdbebd: Fixed bug noticed by Sakib, pointer still at null

[Wouter Deconinck]

  Branch: refs/heads/bugfix-save-all-hits
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  Commit: bdbebd683c44009a975cd69922a312654d3ab7c9
      https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FJeffersonLab%2Fremoll%2Fcommit%2Fbdbebd683c44009a975cd69922a312654d3ab7c9&data=02%7C01%7C12gevmoller_sim%40jlab.org%7Ca447db618ef54c070ff208d6968ed1a9%7Cb4d7ee1f4fb34f0690372b5b522042ab%7C1%7C1%7C636861937478525163&sdata=hKo0GbCYDCKCuys3JYBC%2B8DAVDNiAyKEjzFzf4HyBm8%3D&reserved=0
  Author: Wouter Deconinck <wdconinc at gmail.com>
  Date:   2019-02-19 (Tue, 19 Feb 2019)

  Changed paths:
    M include/remollDetectorConstruction.hh
    M src/remollDetectorConstruction.cc

  Log Message:
  -----------
  Fixed bug noticed by Sakib, pointer still at null

Took me way to long to fix this since I kept overlooking it...

Two new aux helper functions: HasAuxWithType and NextAuxWithType for use
in, for example (in a loop over volumes):
```
G4GDMLAuxListType list = (*iter).second;
if (HasAuxWithType(list,"SensDet")) { /* do something */ }
for (auto it_dettype  = NextAuxWithType(list.begin(), list.end(),
"DetType");
          it_dettype != list.end();
it_dettype  = NextAuxWithType(++it_dettype, list.end(),
"DetType")) { /* do something */ }
```