ndb - bug#29102 : use locked read even for blob parts

ndb/src/ndbapi/NdbBlob.cpp:
  race condition : s/committedRead/readTuple/ when reading parts since TUP commits tuples separately

ndb/src/ndbapi/NdbBlob.cpp

@@ -892,7 +892,12 @@ NdbBlob::readParts(char* buf, Uint32 part, Uint32 count)
   while (n < count) {
     NdbOperation* tOp = theNdbCon->getNdbOperation(theBlobTable);
     if (tOp == NULL ||
-        tOp->committedRead() == -1 ||
+        /*
+         * This was committedRead() before.  However lock on main
+         * table tuple does not fully protect blob parts since DBTUP
+         * commits each tuple separately.
+         */
+        tOp->readTuple() == -1 ||
         setPartKeyValue(tOp, part + n) == -1 ||
         tOp->getValue((Uint32)3, buf) == NULL) {
       setErrorCode(tOp);