[ruby/reline] Return 1 when char width not found

This fixes ruby/reline#261.

3cf1213014

lib/reline/unicode.rb

@@ -108,6 +108,7 @@ class Reline::Unicode
     end
     m = mbchar.encode(Encoding::UTF_8).match(MBCharWidthRE)
     case
+    when m.nil? then 1 # TODO should be U+FFFD <20> REPLACEMENT CHARACTER
     when m[:width_2_1], m[:width_2_2] then 2
     when m[:width_3] then 3
     when m[:width_0] then 0