Add missing Argument null exceptions to post write handlers

src/Tgstation.Server.Host/IO/PosixPostWriteHandler.cs

@@ -1,5 +1,6 @@
 using Mono.Unix;
 using Mono.Unix.Native;
+using System;
 
 namespace Tgstation.Server.Host.IO
 {
@@ -11,6 +12,9 @@ namespace Tgstation.Server.Host.IO
 		/// <inheritdoc />
 		public void HandleWrite(string filePath)
 		{
+			if (filePath == null)
+				throw new ArgumentNullException(nameof(filePath));
+
 			//set executable bit every time, don't want people calling me when their uploaded "sl" binary doesn't work
 			if (Syscall.stat(filePath, out var stat) != 0)
 				throw new UnixIOException(Stdlib.GetLastError());

src/Tgstation.Server.Host/IO/WindowsPostWriteHandler.cs

@@ -1,4 +1,6 @@
-namespace Tgstation.Server.Host.IO
+using System;
+
+namespace Tgstation.Server.Host.IO
 {
 	/// <summary>
 	/// <see cref="IPostWriteHandler"/> for Windows systems
@@ -6,6 +8,10 @@
 	sealed class WindowsPostWriteHandler : IPostWriteHandler
 	{
 		/// <inheritdoc />
-		public void HandleWrite(string filePath) { }
+		public void HandleWrite(string filePath)
+		{
+			if (filePath == null)
+				throw new ArgumentNullException(nameof(filePath));
+		}
 	}
 }