Don't attempt to use an API key if useAccessToken is set, even if an …

…API key exists

lib/webapi.js

@@ -25,7 +25,9 @@ TradeOfferManager.prototype._apiCall = function(httpMethod, method, version, inp
 
 	input = input || {};
 
-	if (this.apiKey) {
+	// We shouldn't strictly need to check useAccessToken here because we wouldn't have an API key anyway, but some
+	// people insist on manually assigning their API key despite the docs telling you not to do that.
+	if (this.apiKey && !this.useAccessToken) {
 		input.key = this.apiKey;
 	} else {
 		input.access_token = this.accessToken;