fixed; callback scope

Author: aheckmann

lib/command.js

@@ -188,7 +188,7 @@ module.exports = function (proto) {
         err = new Error("gm().stream() or gm().write() with a non-readable " +
                         "stream. Pass \"{bufferStream: true}\" to identify() " +
                         "or getter (size, format, etc...)");
-        return cb(this, err);
+        return cb(self, err);
       }
 
       // handle streaming to gm errors when gm/imageMagick is not installed
@@ -198,7 +198,7 @@ module.exports = function (proto) {
         if ('EPIPE' == err.code && 'write' == err.syscall) {
           err.message = missingBinMsg(self) + err.message;
         }
-        cb(this, err);
+        cb(self, err);
       }
 
       self.sourceStream.pipe(proc.stdin);
@@ -239,11 +239,11 @@ module.exports = function (proto) {
           err.code = code;
           err.signal = signal;
         };
-        cb(this, err, stdout, stderr, cmd);
+        cb(self, err, stdout, stderr, cmd);
         stdout = stderr = onOut = onErr = onExit = null;
       });
     } else {
-      cb(this, null, proc.stdout, proc.stderr, cmd);
+      cb(self, null, proc.stdout, proc.stderr, cmd);
     }
 
     return this;