Input merge should copy over the "continue_if_empty" flag
Merge branch 'hotfix/4597'

Close #4597
Merge pull request #4599 from radnan/patch-1

[InputFilter] Input merge should copy over the "continue_if_empty" flag
[#4599] Added test for behavior

- Ensure continueIfEmpty flag is merged
Merge branch 'hotfix/4599' into develop

Forward port #4599

Conflicts:
	tests/ZendTest/InputFilter/InputTest.php