Improve registry backup safety and add optional backup skipping (#710)

Scripts/Features/Backup-RegistrySnapshotCapture.ps1

@@ -201,7 +201,8 @@ function Get-RegistryKeySnapshot {
 
     .DESCRIPTION
         Captures all values or selected value names, records missing selected values,
-        and recursively captures subkeys when requested.
+        and recursively captures subkeys when requested. Throws if a requested subkey
+        cannot be read.
 #>
 function Convert-RegistryKeyToSnapshot {
     param(
@@ -241,7 +242,9 @@ function Convert-RegistryKeyToSnapshot {
     if ($IncludeSubKeys) {
         foreach ($subKeyName in @($RegistryKey.GetSubKeyNames())) {
             $childKey = $RegistryKey.OpenSubKey($subKeyName, $false)
-            if ($null -eq $childKey) { continue }
+            if ($null -eq $childKey) {
+                throw "Unable to read registry subkey '$($RegistryKey.Name)\$subKeyName' while creating a backup snapshot. The backup was not created."
+            }
 
             try {
                 $childPath = if ([string]::IsNullOrWhiteSpace($FullPath)) { $subKeyName } else { "$FullPath\$subKeyName" }