Log controller extension errors.

Before this commit, they would occur silently.

Author: RubenVerborgh

lib/controllers/TriplePatternFragmentsController.js

@@ -41,7 +41,10 @@ TriplePatternFragmentsController.prototype._handleRequest = function (request, r
 
   // Execute the extensions and render the query result
   var extensions = this._extensions, extensionId = 0;
-  (function nextExtension() {
+  (function nextExtension(error) {
+    // Log a possible error with the previous extension
+    if (error)
+      process.stderr.write(error.stack + '\n');
     // Execute the next extension
     if (extensionId < extensions.length)
       extensions[extensionId++].handleRequest(request, response, nextExtension, settings);