Poor error message when files cannot be loaded

[MarkBergman-cbica]

Attempting to open several "dcm" files, CaPTk (1.8.2 non-release) produces the error:

Extensions for the following files were not supported, CaPTk will try to load the rest:

Notes:

• All files had a "dcm" extension.
• No files were listed by name (or extension) in the detail of the error message.
• The comma should be replaced with a semi-colon

Is there really a check by file extension, not the file contents? A DICOM (or NIFTi) file may be perfectly valid and usable within CaPTk regardless of the extension.

[sarthakpati]

@MarkBergman-cbica could you check the files you have with the builds generated by my PR #1431?