Resolve #4590

Author: CasualPokePlayer

src/BizHawk.Emulation.Cores/Consoles/SNK/NeoGeoPort.cs

@@ -53,19 +53,33 @@ public override bool SaveRamModified
 
 		public override byte[] CloneSaveRam(bool clearDirty)
 		{
-			_exe.AddTransientFile(Array.Empty<byte>(), "SAV:flash");
-
-			if (!_neopop.GetSaveRam())
+			_exe.AddTransientFile([ ], "SAV:flash");
+			var success = _neopop.GetSaveRam();
+			var ret = _exe.RemoveTransientFile("SAV:flash");
+			if (!success)
+			{
 				throw new InvalidOperationException("Error returning saveram");
-			return _exe.RemoveTransientFile("SAV:flash");
+			}
+
+			return ret;
 		}
 
 		public override void StoreSaveRam(byte[] data)
 		{
-			_exe.AddTransientFile(data, "SAV:flash");
-			if (!_neopop.PutSaveRam())
+			if (data.Length == 0)
+			{
+				// Empty SaveRAM is valid here, that means at the time of flushing SaveRAM, flash was not attempted to be used yet
+				// The core will reject attempts to put this empty file however, so we must return here
+				return;
+			}
+
+			_exe.AddReadonlyFile(data, "SAV:flash");
+			var success = _neopop.PutSaveRam();
+			_exe.RemoveReadonlyFile("SAV:flash");
+			if (!success)
+			{
 				throw new InvalidOperationException("Core rejected the saveram");
-			_exe.RemoveTransientFile("SAV:flash");
+			}
 		}
 
 		protected override IDictionary<string, SettingOverride> SettingOverrides { get; } = new Dictionary<string, SettingOverride>