Retrieve original does not work for images in root path that start with modifier letter

[hilkeheremans]

The bug:
A call to http://<url>/some/path/cistf72.jpg works fine.
A call to http://<url>/cistf72.jpg does not.

Some investigating revealed that the parse method in modifiers.js calls parseModifiers even when no path is provided. Since the first letter of the filename above is a modifier, it will set the hasModStr variable to true, which in turn cases trouble in image.js.

The end result is that images that (1) are in the root path and (2) start with a filename w/modifier string can never be retrieved by original.