Allow to call JsonSerializationVisitorFactory::setOptions() with value 0

[phansys]

Q	A
Branch	master
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	n/a
License	MIT
Doc PR	n/a

Without these changes, configuring the serializer with the following definition is not possible.

jms_serializer:
    visitors:
        json_serialization:
            options: 0 # json_encode options bitmask, suggested JSON_PRETTY_PRINT in development

[goetas]

Thanks for the PR.

Isn't 0 the default in both of the cases?

[phansys]

Yes, I must improve the tests. The fact is that !empty() with value 0 returns false, so JsonSerializationVisitorFactory::setOptions() is never called with this value. And the default value on that class is 1024.

[phansys]

Tests and PR title updated.

[goetas]

Thanks for contributing