Fix crash for property with case difference and without docblock

[jorrit]

7dc32f5 introduced a possible crash under a very specific situation:

1. A property is matched with a case difference.
2. The property has no docblock

In this situation, the following crash occurs:

Error: Call to a member function hasMethod() on bool[0] (caught throwable) at /var/www/admin/vendor/netresearch/jsonmapper/src/JsonMapper.php line 564.

The reason is that inside inspectProperty(), $class is null when the property is not found by exact name. Later, the code attempts to find the property case-insensitively, but then $class is left false. This leads to a crash in new code introduced by 7dc32f5.

The attached patch contains a test that fails when the change in JsonMapper.php is not applied.

[cweiske]

Thank you for the quick patch.

The unit test did actually not fail because it did not have casing differences in the test data, so I fixed it.
I also split the commit into two, so that the failing test can be run separate from the fix. (Which makes it easier to check if the test indeed fails, and makes finding the culprit very easy)

Released with 4.4.1