When implementing new build variants for UBSAN in
WT-7552, a number of errors of the following signature were detected in src/txn/txn_ckpt.c:
The offending line is as follows:
The reason for this error is that an uninitialized bool will have an indeterminate value, which is undefined behavior. The seen_ckpt_add variable is not initialized until late in the function and there are code paths that would skip this initialization completely. Moving the variable initialization to earlier in the function would prevent this sanitizer error.