mtr/basic/t/unsigned_join test works incorrectly on Centos8 and results of different runs are different

The test mentioned above fails under Centos8 - and only there. Other Linux distros appear unaffected.

Apart from that, second run of the same test shows different results.

The problem appears to be extents ranges that are not set into valid ranges with at least one value in them and also set to CP_VALID. When test is augmented with selection from information_schema.columnstore_extents the ranges have status "Valid" and min and max values are NULLs.

It appears that LOAD TABLE statement does not do the job.