Format inference with buffers and streams

[adurrive]

There is no format inference from the filename for input buffers or streams. Format inference from the file signature doesn't work with some formats like ico:

gm('/path/to/img.ico').size(function (err, size) { ...  });

{ width: 64, height: 64 }

buffer = fs.readFileSync('/path/to/img.ico');
gm(buffer, 'img.ico').size(function (err, size) { ...  }); 

stream = fs.createReadStream('/path/to/img.ico');
gm(stream, 'img.ico').size({bufferStream: true}, function (err, size) { ...  }); 

{ [Error: Command failed: gm identify: No decode delegate for this image format (/tmp/gm3mwq).
gm identify: Request did not return an image.
] code: 1, signal: null }

[adurrive]

Fixed by #430

[freund17]

There is no format inference from the filename for input buffers or streams. 

I created a PR for that: #701