Fix issues with retrieving process memory

src/Tgstation.Server.Host/Components/Session/SessionController.cs

@@ -122,7 +122,7 @@ namespace Tgstation.Server.Host.Components.Session
 		public FifoSemaphore TopicSendSemaphore { get; }
 
 		/// <inheritdoc />
-		public long MemoryUsage => process.MemoryUsage;
+		public long? MemoryUsage => process.MemoryUsage;
 
 		/// <summary>
 		/// The <see cref="Byond.TopicSender.ITopicClient"/> for the <see cref="SessionController"/>.

src/Tgstation.Server.Host/System/IProcessBase.cs

@@ -16,7 +16,7 @@ namespace Tgstation.Server.Host.System
 		/// <summary>
 		/// Gets the process' memory usage in bytes.
 		/// </summary>
-		long MemoryUsage { get; }
+		long? MemoryUsage { get; }
 
 		/// <summary>
 		/// Set's the owned <see cref="global::System.Diagnostics.Process.PriorityClass"/> to a non-normal value.

src/Tgstation.Server.Host/System/Process.cs

@@ -23,7 +23,21 @@ namespace Tgstation.Server.Host.System
 		public Task<int?> Lifetime { get; }
 
 		/// <inheritdoc />
-		public long MemoryUsage => handle.VirtualMemorySize64;
+		public long? MemoryUsage
+		{
+			get
+			{
+				try
+				{
+					return handle.VirtualMemorySize64;
+				}
+				catch (Exception ex)
+				{
+					logger.LogWarning(ex, "Failed to get PID {pid}'s memory usage!", Id);
+					return null;
+				}
+			}
+		}
 
 		/// <summary>
 		/// The <see cref="IProcessFeatures"/> for the <see cref="Process"/>.