Trailing uninit mem in schema project

The ex_col_store.c program from WT-7072 fails when compiled with the memory sanitiser. This is likely an internal problem not providing column store support. 

Here is the link to the evergreen error https://evergreen.mongodb.com/task/wiredtiger_ubuntu1804_make_check_msan_test_48fd16f2247101b2af46661adeb3bfa37e2f9e63_21_01_28_02_50_31

Steps to reproduce:

1. Use the minimal reproducer (example_file.c) in the attachment.
2. Set CC=clang CFLAGS="-fsanitize=memory" ../configure

Acceptance criteria:

Allow ex_col_store.c to run with memory sanitiser enabled.