Avoid setenv on blank lines

Author: weikanglim

scripts/prepdocs.ps1

@@ -5,6 +5,10 @@ Write-Host ""
 $output = azd env get-values
 
 foreach ($line in $output) {
+  if (!$line.Contains('=')) {
+    continue
+  }
+
   $name, $value = $line.Split("=")
   $value = $value -replace '^\"|\"$'
   [Environment]::SetEnvironmentVariable($name, $value)