Return sooner from _decode when $hash is undef

Note that we test for definedness, not for truthiness: a $hash of "0"
should still count as valid, to prevent issues like found in #7.
Tidy up
Minilla files regen
Checking in changes prior to tagging of version 1.000001.

Changelog diff is:

diff --git a/Changes b/Changes
index de78633..1cb809e 100644
--- a/Changes
+++ b/Changes
@@ -2,6 +2,11 @@ Revision history for Perl extension Hashids

 {{$NEXT}}

+1.000001 2014-12-04T06:54:57Z
+
+    - Fix issue where some hashes could not be decoded, thanks to
+      C. A. Church (closes #7)
+
 1.000000 2014-09-10T13:00:52Z

     - Bump to 1.0.0 hashids.js API, closes #5