Don't throw exception when trying to encrypt falsey value.
Merge pull request #2483 from ADmad/2.5-security

Don't throw exception when trying to encrypt falsey value.
Revert change done in 11f543f1f2.

The change is unneeded now as Security::encrypt() no longer throws exception
for falsey values.
Merge pull request #2484 from ADmad/2.5-cookiecomponent

Revert change done in 11f543f1f2.
Merge remote-tracking branch 'origin/2.5' into 3.0

Conflicts:
	Cake/Test/TestCase/Utility/SecurityTest.php
	Cake/Utility/Security.php