Error Isolating Nested Template Lines

Same repro as in #583 (found this while testing that on 2022.03.04)

Running the TTK over the test folder in the quickstart repo shows the error below. To repro put an empty template azuredeploy.json file in the test folder and run the command:

Test-AzTemplate -templatePath ./azuredeploy.json/
or
Test-AzTemplate test #from the parent folder

azuredeploy.json contents:
```json
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": { },
"variables": { },
"resources": [ ],
"outputs": { }
}
```

The following error appears multiple times in the output.

```
Write-Error: C:\Users\bmoore\source\repos\arm-ttk\arm-ttk\Test-AzTemplate.ps1:629
Line |
629 | Test-Group
| ~~~~~~~~~~
| Error Isolating Nested Template Lines in ModularTemplateWithMetadata.json
```