Block's `OpenBraceRange.Start` differs if a proper block precedes it or not

I have two different HCL blocks.
```HCL
variable bad
{}
```
```HCL
variable good {}
variable bad
{}
```
Although both of the `bad` blocks look similar, their `Block.OpenBraceRange.Start` value is quite different. The first one seems to believe it exists at the start of the file (essentially `hcl.InitialPos`) but the second one seems to have something more sane as a response.
```
{1 1 0}
{2 1 17}
```
```Go
package main

import (
"fmt"

"github.com/hashicorp/hcl/v2"
"github.com/hashicorp/hcl/v2/hclsyntax"
)

func Parse(filename string, bytes []byte) *hclsyntax.Body {
file, _ := hclsyntax.ParseConfig(bytes, filename, hcl.InitialPos)
return file.Body.(*hclsyntax.Body)
}

func main() {
body := Parse("", []byte("variable bad\n{}"))
fmt.Println(body.Blocks[0].OpenBraceRange.Start)

body = Parse("", []byte("variable good {}\nvariable bad\n{}"))
fmt.Println(body.Blocks[1].OpenBraceRange.Start)
}
```

Start by running the supplied Go reproduction through hclsyntax.ParseConfig and inspect how Block.OpenBraceRange.Start is assigned. Trace the parser's handling of the two block layouts, then add regression coverage showing that equivalent blocks report the correct brace position.

Written by the indexing model from the issue text.