An additional check on the length of the requested substring has to be done, otherwise a std::exception is thrown when std::string::substr( -1 ) is called.

With this fix, however, the mitkPointSetReaderTest is still failing (the reader is not recognized) since the test is asking for

readerRegistry.GetReaders(mitk::FileReaderRegistry::GetMimeTypeForFile("mps"));

Which then does not match by the "."+"mps" expression. So we need to clarify, whether the test is asking for a MimeType with an invalid path and hence returning 'false' is valid here, or not.

The API of the method is as follows

FileReaderRegistry::GetMimeTypeForFile(const std::string& path, us::ModuleContext*)

and similarly for the affected method itself

CustomMimeType::ParsePathForExtension(const std::string& path, std::string& extension, std::string& filename ) const

This can be interpreted in a way that the "path" string should contain a valid path ( i.e. including the extension ) which is not the case for the PointSetTest.

Removed CM-Flag until this is solved just to be on the safe side. :)