libicon: Fix leak of Icon::Gradient.

This was most prominently visible in applications that show a lot of
icons like Tracker and Deskbar.

src/libs/icon/style/Style.cpp

@@ -223,6 +223,7 @@ Style::SetGradient(const ::Gradient* gradient)
 #endif
 		delete[] fColors;
 		delete[] fGammaCorrectedColors;
+		delete fGradient;
 		fColors = NULL;
 		fGammaCorrectedColors = NULL;
 		fGradient = NULL;