Special characters in user agent strings cause HTTP corruption

Passing any special characters via DSN `client_string` parameter will cause HTTP headers to be incorrectly sized, and the generated request to be corrupted.  This appeared in Node.js v11, where the openSSL version contained a space and newline at the end.  I've included the specific client_string which caused the failure below:

client_string=couchnode%2F2.6.0%20(node%2F11.0.0%3B%20v8%2F7.0.276.28-node.5%3B%20ssl%2F1.1.0i%20%0A)