More Vi/NvFlinger/NvDrv stubs, allow paths starting with //, do not allow paths that don't start with at least a /, increase map region size

Ryujinx.Core/VirtualFs.cs

@@ -18,10 +18,18 @@ namespace Ryujinx.Core
 
         public string GetFullPath(string BasePath, string FileName)
         {
-            if (FileName.StartsWith('/'))
+            if (FileName.StartsWith("//"))
+            {
+                FileName = FileName.Substring(2);
+            }
+            else if (FileName.StartsWith('/'))
             {
                 FileName = FileName.Substring(1);
             }
+            else
+            {
+                return null;
+            }
 
             string FullPath = Path.GetFullPath(Path.Combine(BasePath, FileName));