- fixed render backend switch menu option

wadsrc/static/menudef.txt

@@ -1490,6 +1490,14 @@ OptionValue GPUSwitch
 	2.0, "$OPTVAL_INTEGRATED"
 }
 
+OptionValue PreferBackend
+{
+	0, "$OPTVAL_OPENGL"
+	1, "$OPTVAL_VULKAN"
+	// Enable when HAVE_SOFTPOLY will be defined
+	//2, "$OPTVAL_SOFTPOLY"
+}
+
 OptionMenu VideoModeMenu protected
 {
 	Title "$VIDMNU_TITLE"