Issue on empty param

The function returns "31/12/1969 21:00:00" when pass empty date param.
Fix TimeHelper returning 1969 on invalid dates.

Instead of returning 1969, TimeHelper should return the invalid date,
and if that is missing '' should be returned.

Fixes #4294
Merge branch 'issue-4294' into 1.3
Removed all occurences of crc32 in dbo_source as a cache key,
 which is not only a stupid idea but should be actually considered a bug!
It does collide with a .1% propability for every 1.6mio queries processed
(which is not to uncommon in a shell process).
Removed crc32() because of *very* common collisions occuring.

Does not touch any of the exposed stuff and will not break anything
else (except you know of a collision within crc32 already and make
"use" of it - which can only be malcious.)

Has already been "fixed" in the 2.x branch.
Merge pull request #4368 from hmic/1.3-dbo_source-NO-crc32

1.3 dbo source no crc32