speed up GL_SetPalette "take 2"

ensuring bytecolor is packed nd mypalettedata is initialized this seems to now work properly on windows

src/hardware/r_opengl/r_opengl.c

@@ -1499,14 +1499,14 @@ void GL_ReadScreenTexture(int tex, UINT8 *restrict dest, INT32 scale)
 // -----------------+
 void GL_SetPalette(RGBA_t *palette)
 {
-	INT32 i;
+	const size_t palsize = (sizeof(RGBA_t) * 256);
 
-	for (i = 0; i < 256; i++)
+	// on a palette change, you have to reload all of the textures
+	if (memcmp(myPaletteData, palette, palsize))
 	{
-		myPaletteData[i].s = palette[i].s;
+		memcpy(myPaletteData, palette, palsize);
+		GL_Flush();
 	}
-
-	GL_Flush();
 }
 
 // -----------------+