Update install-windows.bat to not exit command prompt on error (#37)

The '/b' switch will exit the current script, but not close the command prompt.

install-windows.bat

@@ -5,13 +5,13 @@ cd /d "%~dp0"
 if exist SwarmUI (
     echo SwarmUI is already installed in this folder. If this is incorrect, delete the 'SwarmUI' folder and try again.
     pause
-    exit
+    exit /b
 )
 
 if exist SwarmUI.sln (
     echo SwarmUI is already installed in this folder. If this is incorrect, delete 'SwarmUI.sln' and try again.
     pause
-    exit
+    exit /b
 )
 
 winget install Microsoft.DotNet.SDK.8 --accept-source-agreements --accept-package-agreements