jones-ndb: assertion fails on getNoOfBlobColumns

[jdduncan]

In part of the issue#37 we see:
Assertion `nblobs == record->getNoOfBlobColumns()' failed

[jdduncan]

Also:

Assertion failed: ((col->flags & NdbRecord::IsBlob) == 0), function unpackNdbRecord, file /Users/jdd/git-work-trees/working/mysql-5.7-cluster-7.5/storage/ndb/src/ndbapi/NdbReceiver.cpp, line 1003.

[jdduncan]

The issue here is that jones-ndb is executing the join query using SPJ, but SPJ does not support BLOBs.