handle situation where line from password file does not match regex

NEWS

+unreleased (2014-04-??)
+
+    Fix error if line read from password file does not match
+    regular expression. (adamhl)
+
 release/001.001 (2014-03-17)
 
     Added the custom facts "regular_users" and "root_users". See the file

lib/facter/users.rb

@@ -16,7 +16,7 @@ Facter.add("regular_users") do
       lines.each do |l|
         #          games:x:5:60:games:/usr/games:/bin/sh
         match = /^([^:]+):([^:]+):(\d+):(\d+):/.match(l)
-        if (match.length >= 3)
+        if ((!match.nil?) && match.length >= 3)
           name  = match[1]
           id    = match[3]
           group = match[4]