Coverity link: https://coverity.corp.mongodb.com/#/project-view/24224/10049?selectedIssue=207629

In __wt_block_read_off_blind():

WT_ERR(__wt_read(session, block->fh, offset, (size_t)block->allocsize, tmp->mem));

block->fh is dereferenced but potentially could be NULL.

Reproducer: https://jira.mongodb.org/secure/attachment/1396962/test_inmem04.py

Verify can crash when dumping blocks of an in-memory table, because that table has no file on disk to read from. The code tries to read anyway, hits a null file handle, and the process dies.