Mimetypes v3: Fix that octet-stream was wrongly considered parent

The fallback mimetype of application/octet-stream is supposed to only be
a fallback if the mimetype doesn't specify another parent.

Amends 98b1e82d2b

Fixes: QTCREATORBUG-27398
Change-Id: I4ac92dd4817fae37de4499fe9e08aa2e5dd50a51
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/utils/mimetypes2/mimedatabase.cpp

@@ -356,9 +356,11 @@ QStringList MimeDatabasePrivate::parents(const QString &mimeName)
             break;
         }
     }
+    if (result.isEmpty()) {
         const QString parent = fallbackParent(mimeName);
         if (!parent.isEmpty())
             result.append(parent);
+    }
     return result;
 }