Fix case that there is no '.pause'.

`Config::Identity::PAUSE->load` returns nothing without exception
if there is no pause configuration file like `~/.pause`. In such
case, eval block returns true, but uninitialized value reference
is arisen because `$pause{user}` is `undef`.
Merge pull request #126 from tokuhirom/fix-for-no-dot-pause

Fix case that there is no '.pause'.