Fix GenericIO reader issue with multiple timesteps

The GenericIO reader was resetting the DataArraySelection
object when the filename was changed. Consequently, all arrays
were disabled and if the user has loaded arrays in the previous
time-step, they would not be loaded in later time-steps. Fixed that.

Change-Id: I67fffdb69a21c1f8c7e7b701ade0423fbbc2f5b1
Merge topic 'fix-genericio-fileseries-reader' into next

9d540ab Fix GenericIO reader issue with multiple timesteps