Callback upon error and exception handling

[jolks]

This is to allow color extraction to still continue working in case of error or exception.

In parseHistogramLine function, when gm does not fully remove the EXIF data, error such as Cannot read property 'split' of undefined will occur. The EXIF data looks like [ 'EXIF', 'Orientation={1' ].

Regardless of the EXIF data are there or not, exception handler will help.