Catch Throw in Series Ctor/Dtor

[ax3l]

Destructors must not throw, which would abort e.g. if flush() reports a late problem in ~Series or a backend's ~...IOHandler.
Constructors can throw, but we must be able to catch this.

Typical problem: read-only opening of non-existent files throws in Ctor as it flushes all reads.

[guj]

this does not not necessarily catch the exception from. ~ADIOS2IOHandler(){ flush();}

rather may have caught "fileBased output can not be written with no iterations"
from Series::flushFileBased() first.

[ax3l]

Thank you Junmin! Totally overlooked these.

[guj]

Would it be possible to move the code in *.hpp to *.cpp?

[ax3l]

For ADIOS2IOHandler.hpp? Yes, good idea.

[ax3l]

Checked again: we build a defaulted destructor and no member vars in the case ADIOS2 is not enabled, so keeping this in the header is fine here.