Fix assertion (off-by-one)
Ensure NSSpellChecker methods are called from main queue

I have been told that the spell checker should be thread safe (except for the spelling panel) but after moving to concurrent execution of the integration tests, several segmentation faults have pointed toward the spell checker not being thread safe.
Explicitly run libcurl’s global init function

This function is not thread safe so we should not have it implicitly called, as we generally do not call the libcurl functions from the main thread.