Fix unknown encoding (dj2#12)

Verify that the given encoding is valid before using.

lib/ruby-rtf/parser.rb

@@ -126,7 +126,15 @@ def handle_control(name, val, src, current_pos)
       case(name)
       when :rtf then ;
       when :deff then @doc.default_font = val
-      when :ansicpg then self.encoding = "windows-#{val}"
+      when :ansicpg then
+        begin
+          # Set the encoding if it's valid
+          Encoding.find("windows-#{val}")
+          self.encoding = "windows-#{val}"
+        rescue => e
+          # ignore
+        end
+
       when *[:ansi, :mac, :pc, :pca] then @doc.character_set = name
       when :fonttbl then current_pos = parse_font_table(src, current_pos)
       when :colortbl then current_pos = parse_colour_table(src, current_pos)

lib/ruby-rtf/version.rb

@@ -1,5 +1,5 @@
 # Main namespace of the RTF parser
 module RubyRTF
   # Current library version
-  VERSION = '0.0.4'
+  VERSION = '0.0.5'
 end