Omitting `:one` or `:many` causes a panic

[inconshreveable]

Validation of the magic comment is not quite right. If you omit the directive of how the query should be handled, sqlc panics:

panic: runtime error: index out of range

goroutine 1 [running]:
github.com/kyleconroy/sqlc/internal/dinosql.parseMetadata(0xc0004c02c0, 0x52, 0x900b60, 0xc00000e760, 0x0, 0x52, 0xc0004c02c0, 0x52)
	/home/runner/work/sqlc/sqlc/internal/dinosql/parser.go:294 +0x1e7
github.com/kyleconroy/sqlc/internal/dinosql.parseQuery(0xc00017a030, 0x900b60, 0xc0004cffc0, 0xc0004c02c0, 0x145, 0x0, 0x0, 0x0)
	/home/runner/work/sqlc/sqlc/internal/dinosql/parser.go:322 +0x2cb
github.com/kyleconroy/sqlc/internal/dinosql.ParseQueries(0xc00017a030, 0xc0000deea0, 0x1, 0x4, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/runner/work/sqlc/sqlc/internal/dinosql/parser.go:210 +0x6e6
github.com/kyleconroy/sqlc/internal/cmd.glob..func4(0xe0db40, 0xe3e5a8, 0x0, 0x0)
	/home/runner/work/sqlc/sqlc/internal/cmd/cmd.go:142 +0x9b7
github.com/spf13/cobra.(*Command).execute(0xe0db40, 0xe3e5a8, 0x0, 0x0, 0xe0db40, 0xe3e5a8)
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:830 +0x2ae
github.com/spf13/cobra.(*Command).ExecuteC(0xc000160280, 0xc0000bbf20, 0x1, 0x1)
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:914 +0x2fc
github.com/spf13/cobra.(*Command).Execute(...)
	/home/runner/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:864
github.com/kyleconroy/sqlc/internal/cmd.Do(0xc0000a0010, 0x1, 0x1, 0x8fac60, 0xc00009a000, 0x8fac80, 0xc00009a008, 0x8fac80, 0xc00009a010, 0xc000080058)
	/home/runner/work/sqlc/sqlc/internal/cmd/cmd.go:33 +0x24a
main.main()
	/home/runner/work/sqlc/sqlc/cmd/sqlc/main.go:10 +0xab

Test case:

-- name: ListFlags
SELECT * FROM flag;