[3.6] WT error handler incorrectly prints "An unsupported journal format detected"

The logic in the WT error handler in MongoDB is the inverse of what it should be.

We evaluate if StringData::find() returns non-zero. Instead we should evaluate that it is not equal to std::string::npos, or -1.

This can confusingly report "An unsupported journal format detected" for all unrelated WiredTiger errors, except for the error it intends on detecting.

This was caused by a backport of SERVER-35271.