Ignore case with data file extensions

[flipvis]

ScribusGenerator/ScribusGeneratorBackend.py

Line 213 in 24518a7

extension = os.path.splitext(data_file)[1]

This way of determining data file extension is case-sensitive. Meaning that datafile.CSV doesn't get processed at all. This also doesn't raise an error. Only indication that this has happened is a line in the log:
ScribusGenerator - INFO: Source document consumes 1 data record(s) from 0.

A quick fix could be adding a .lower()

extension = os.path.splitext(data_file)[1] .lower()

[flipvis]

Arguably this is a rather lazy fix. Potentially the code should check whether any valid extension is found, and if no valid extension is found, raise an error?