xdg-mime-apps: fix regex in mimeAssociations

The XDG Desktop Entry spec mentions that multiple values per key may be
optionally terminated by a semicolon. An example for this is the Firefox
desktop file, which has no trailing semicolon. This breaks the sed regex
used in `mimeAssociations`.

Fix the regex by matching the end of string, optionally preceded by a
semicolon, or any other semicolon. This makes it work with both
semicolon-terminated and non-semicolon-terminated desktop files.

modules/misc/xdg-mime-apps.nix

@@ -94,7 +94,7 @@ in {
             for p in $ps ; do
               for path in "$p"/share/applications/*.desktop ; do
                 name="''${path##*/}"
-                sed -n "/^MimeType=/ { s/.*=//; s/;/;$name\n/g; p; }" "$path"
+                sed -n -E "/^MimeType=/ { s/.*=//; s/;?$|;/;$name\n/g; p; }" "$path"
               done
             done > "$out"
           '';