Update RomLoader.cs

Fixes #865

BizHawk.Client.Common/RomLoader.cs

@@ -317,6 +317,15 @@ namespace BizHawk.Client.Common
 					}
 					else
 					{
+						// at this point, file is either assigned to the ROM path, if it exists,
+						// or is empty and corecomm is not a libretro core
+						// so, we still need to check path here before continuing
+						if (string.IsNullOrEmpty(path))
+						{
+							Console.WriteLine("No ROM to Load");
+							return false;
+						}
+						
 						// if not libretro:
 						// do extension checknig
 						ext = file.Extension.ToLowerInvariant();