Enhance error detection and fix other issues in unionvtab code.
FossilOrigin-Name: 9c3f1b9a82e500e015deb0cc669fbb32e7f0cdc69f926ceff383ab946f8d8d18
D
dan committed
bcd303ac7d62a7ba2df2d3a8a73f9e7031b61f71
Parent: d8ecefa
FossilOrigin-Name: 9c3f1b9a82e500e015deb0cc669fbb32e7f0cdc69f926ceff383ab946f8d8d18