VIEWreset: cope with mirrored BAT input
VIEWreset: cope with mirrored BAT input

Since BATins no longer accepts non-(v)oid-headed input, it is important
that we call BATins with head and tail in the order as the caller
provided, not to get unexpected GDKerrors from higher-levels.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb