Try to prevent more memory leaks by using .once and cleaning up event…

… listeners on error and premature close.

lib/processImage.js

@@ -71,8 +71,13 @@ module.exports = function (options) {
                                 if (filter.end) {
                                     filter.end();
                                 }
+                                filter.removeAllListeners();
+                                // Some of the filters seem to emit error more than once sometimes:
+                                filter.on('error', function () {});
                             });
+                            filters = null;
                         }
+                        res.removeAllListeners();
                     }
                 }
 
@@ -152,19 +157,21 @@ module.exports = function (options) {
                         filters[i].on('etagFragment', function (etagFragment) {
                             etagFragments.push(etagFragment);
                         });
-                        filters[i].on('error', handleError);
+                        // Some of the filters appear to emit error more than once:
+                        filters[i].once('error', handleError);
                     }
 
                     res.pipe(filters[0]);
                     filters[filters.length - 1].on('end', function () {
                         hasEnded = true;
+                        cleanUp();
                     }).pipe(res);
 
-                    res.on('error', function () {
+                    res.once('error', function () {
                         res.unhijack();
                         next(500);
                     });
-                    res.on('close', cleanUp);
+                    res.once('close', cleanUp);
                 } else {
                     res.unhijack();
                 }