Mimedatabase: Fix inherits and collecting parents

Amends 377198641c

The DuplicateTracker needs to return true for `hasSeen` if the value was
*not* inserted.

Change-Id: Id4ddc75b5a5a8d33094c358687766115dd5f6384
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/mimetypes2/mimedatabase.cpp

@@ -43,7 +43,7 @@ namespace Utils {
 template <typename T>
 class DuplicateTracker {
 public:
-    bool hasSeen(const T &v) { return Utils::insert(seen, v); }
+    bool hasSeen(const T &v) { return !Utils::insert(seen, v); }
 private:
     QSet<T> seen;
 };