don't crash if the PDF incorrectly uses vertical mode

(found example of pdf that used vertical mode with
a font that didn't support vertical mode)

lib/pdf/reader/width_calculator/built_in.rb

@@ -46,6 +46,13 @@ def glyph_width(code_point)
         m ? m[:wx] : 0
       end
 
+      #TODO: no idea why my pdf is using a built-in font in 
+      #vertical writing mode. Couldn't find anything in the
+      #spec that described the desired behavior in this case.
+      def glyph_height(code_point)
+        return 0
+      end
+
     end
   end
 end

lib/pdf/reader/width_calculator/true_type.rb

@@ -50,6 +50,13 @@ def glyph_width_from_descriptor(code_point)
           nil
         end
       end
+
+      #TODO: figure out the proper response when the pdf
+      #tries to write in vertical mode with this font
+      #(which doesn't support vertical mode)
+      def glyph_height(code_point)
+        return 0
+      end
     end
   end
 end

lib/pdf/reader/width_calculator/type_one_or_three.rb

@@ -27,6 +27,13 @@ def glyph_width(code_point)
           @missing_width.to_f
         end
       end
+
+      #TODO: figure out the proper response when the pdf
+      #tries to write in vertical mode with this font
+      #(which doesn't support vertical mode)
+      def glyph_height(code_point)
+        return 0
+      end
     end
   end
 end