[font] Fix design-coords

Ouch!

src/hb-font.cc

@@ -2387,6 +2387,10 @@ hb_font_set_variations (hb_font_t            *font,
     return;
   }
 
+  /* Initialize design coords to default from fvar. */
+  for (unsigned int i = 0; i < coords_length; i++)
+    design_coords[i] = axes[i].get_default ();
+
   for (unsigned int i = 0; i < variations_length; i++)
   {
     const auto tag = variations[i].tag;

src/hb-ot-var-fvar-table.hh

@@ -135,7 +135,6 @@ struct AxisRecord
     return_trace (c->check_struct (this));
   }
 
-  protected:
   void get_coordinates (float &min, float &default_, float &max) const
   {
     default_ = defaultValue / 65536.f;
@@ -144,6 +143,11 @@ struct AxisRecord
     max = hb_max (default_, maxValue / 65536.f);
   }
 
+  float get_default () const
+  {
+    return defaultValue / 65536.f;
+  }
+
   public:
   Tag		axisTag;	/* Tag identifying the design variation for the axis. */
   protected: