Fix build with freetype 2.13.3

Index: font_freetype/agg_font_freetype.cpp
--- font_freetype/agg_font_freetype.cpp.orig
+++ font_freetype/agg_font_freetype.cpp
@@ -186,7 +186,7 @@ namespace agg
             v_control = v_start;
 
             point = outline.points + first;
-            tags  = outline.tags  + first;
+            tags  = reinterpret_cast<char*>(outline.tags)  + first;
             tag   = FT_CURVE_TAG(tags[0]);
 
             // A contour cannot start with a cubic control point!
