trying to fix handling file storages with extremely long lines

* trying to fix handling of file storages with extremely long lines: https://github.com/opencv/opencv/issues/11061

* * fixed errorneous pointer access in JSON parser.
* it's now crash-test time! temporarily set the initial parser buffer size to just 40 bytes. let's run all the test and check if the buffer is always correctly resized and handled

* fixed pointer use in JSON parser; added the proper test to catch this case

* fixed the test to make it more challenging. generate test json with
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etc. shape