Fix -Wnon-virtual-dtor compiler warnings.

core/include/fxge/fx_dib.h

Index: core/include/fxge/fx_dib.h
diff --git a/core/include/fxge/fx_dib.h b/core/include/fxge/fx_dib.h
index d8a2003548c8bee1739405ab79e62a056390554c..f7e435d9663a5699ec76049e5a016347bdbef0ea 100644
--- a/core/include/fxge/fx_dib.h
+++ b/core/include/fxge/fx_dib.h
@@ -402,16 +402,15 @@ protected:
 class IFX_ScanlineComposer
 {
 public:
+    virtual ~IFX_ScanlineComposer() { }
 
     virtual	void		ComposeScanline(int line, FX_LPCBYTE scanline, FX_LPCBYTE scan_extra_alpha = NULL) = 0;
 
-
     virtual FX_BOOL		SetInfo(int width, int height, FXDIB_Format src_format, FX_DWORD* pSrcPalette) = 0;
 };
 class CFX_ScanlineCompositor : public CFX_Object
 {
 public:
-
     CFX_ScanlineCompositor();
 
     ~CFX_ScanlineCompositor();