Avoid duplicates in the available backends list
Review Request #129791 - Created Jan. 8, 2017 and submitted - Latest diff uploaded
If a generator can open two mime types that match the same file, okular will show a selection dialog containing two copies of the same generator when opening that file. This patch avoids having duplicates in the backend list.
Tried opening a PDF, okular opens it directly. Before this patch, if the "Show backend selection dialog" option was enabled, it would show a backend selection dialog with two copies od the poppler generator.