Fix -Wnon-virtual-dtor compiler warnings.

core/include/fxcrt/fx_stream.h

Index: core/include/fxcrt/fx_stream.h
diff --git a/core/include/fxcrt/fx_stream.h b/core/include/fxcrt/fx_stream.h
index 8e298f772754cc6626ed0c81a0dfc76e4ccab0f5..e54af579b62c576a9b9f575a3bdebe06f477a7a3 100644
--- a/core/include/fxcrt/fx_stream.h
+++ b/core/include/fxcrt/fx_stream.h
@@ -65,7 +65,7 @@ FX_BOOL		FX_File_Move(FX_WSTR fileNameSrc, FX_WSTR fileNameDst);
 class IFX_StreamWrite
 {
 public:
-
+    virtual ~IFX_StreamWrite() { }
     virtual void		Release() = 0;
 
     virtual	FX_BOOL		WriteBlock(const void* pData, size_t size) = 0;
@@ -91,6 +91,7 @@ IFX_FileWrite* FX_CreateFileWrite(FX_LPCWSTR filename);
 class IFX_StreamRead
 {
 public:
+    virtual ~IFX_StreamRead() { }
 
     virtual void			Release() = 0;
 
@@ -103,7 +104,6 @@ public:
 class IFX_FileRead : IFX_StreamRead
 {
 public:
-
     virtual void			Release() = 0;
 
     virtual FX_FILESIZE		GetSize() = 0;