IndentedStringBuilder shouldn't create space-only lines

# Steps

``` C#
var builder = new IndentedStringBuilder();
using (builder.Indent())
    builder.AppendLine();
return builder.ToString();
```
# Result

``` C#
"    \r\n"
```
# Expected

``` C#
"\r\n"
```

The extra characters are a waste of _space_. :wink: We currently use `IndentedStringBuilder` in the following areas.
- Migrations
  - Code
  - DDL
- Query
  - SQL
