Fix bug in File loader plugin selection.

Bug example: OVM loads *.volumemesh files, however the previous logic would also try to use this plugin to load a *.mesh file, because "mesh" is a suffix of "volumemesh"

This change adopts the same logic exhibited in Core/openFunctions.cc to require an advertised filetype to have a suffix of "*.ext", not of "ext" when trying to load a file "foo.ext".