Bug 471247

SUMMARY
When selecting a LUT file Kdenlive only lists .cube files even though there are many .CUBE files in the same directory. (I haven't tested this behavior on other file formats and suffixes)
Once a LUT file is selected all the other LUT files in the same directory and with the previously not recognized file suffix .CUBE are available in the LUT file drop-down list

STEPS TO REPRODUCE
1. Open the LUT file to apply drop-down in the Apply LUT effect
2. Navigate to the folder where LUT files are stored
3. Select a LUT file

OBSERVED RESULT
1. Not all LUT files are listed in the file open dialog
2. Once the only listed LUT file is opened, all other LUT files in the same folder are available in the drop-down list

EXPECTED RESULT
1. All LUT files with supported formats/file extensions are listed regardless of upper-/lowercase spelling of the suffix (e.g., .CUBE and .cube should be treated the same)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Pop!_OS 22.04
KDE Frameworks Version:  5.92.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
MLT Version: 7.16.0