Fix of GH#43 Assertion Fail for localGridIndex

The grid number associated with an ert grid was an ID and not an index.
In addition: Fixed unrobustness handling wells with no data.
Now the /Troll/MSW_LGR/2BRANCHES-CCEWELLPATH-NEW-SCH-TUNED-AR3.EGRID file loads( Have tested only two timesteps ).
p4#: 22321

ApplicationCode/ReservoirDataModel/RigGridBase.cpp

@@ -33,10 +33,12 @@ RigGridBase::RigGridBase(RigMainGrid* mainGrid):
     if (mainGrid == NULL)
     {
         m_gridIndex = 0;
+        m_gridId    = 0;
     }
     else
     {
         m_gridIndex = cvf::UNDEFINED_SIZE_T;
+        m_gridId = cvf::UNDEFINED_INT;
     }
 }