panic during `dolt dump`if db contains a (non-empty) table with virtual columns

[nicktobey]

Repro:

dolt init
dolt sql -q "create table test(pk int primary key, g int as (pk*pk));"
dolt sql -q "insert into test(pk) values (1);"
dolt dump -f -fn ~/dump.sql

Expected output: Successfully exported data.

Actual output:

panic: runtime error: index out of range [0] with length 0

goroutine 39 [running]:
github.com/dolthub/dolt/go/libraries/doltcore/schema.(*ColCollection).GetByIndex(...)
	/Users/nick/Documents/dolt/go/libraries/doltcore/schema/col_coll.go:246
github.com/dolthub/dolt/go/libraries/doltcore/sqle/sqlfmt.SqlRowAsTupleString({0x140011897c0?, 0x2, 0x14000c31e68?}, {0x1032c3940, 0x140011a0700})
	/Users/nick/Documents/dolt/go/libraries/doltcore/sqle/sqlfmt/row_fmt.go:341 +0x340
github.com/dolthub/dolt/go/libraries/doltcore/table/untyped/sqlexport.(*BatchSqlExportWriter).WriteSqlRow(0x1400091bd90, {0x1032284c8?, 0x140009d44b0?}, {0x140011897c0, 0x2, 0x2})
	/Users/nick/Documents/dolt/go/libraries/doltcore/table/untyped/sqlexport/batch_sqlwriter.go:123 +0x198
github.com/dolthub/dolt/go/libraries/doltcore/mvdata.(*DataMoverPipeline).Execute.func2()
	/Users/nick/Documents/dolt/go/libraries/doltcore/mvdata/pipeline.go:87 +0xf0
golang.org/x/sync/errgroup.(*Group).Go.func1()
	/Users/nick/go/pkg/mod/golang.org/x/[email protected]/errgroup/errgroup.go:78 +0x58
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 1
	/Users/nick/go/pkg/mod/golang.org/x/[email protected]/errgroup/errgroup.go:75 +0x98