Define add button as default in torrent addition dialog

src/torrentadditiondlg.cpp

@@ -64,6 +64,8 @@ torrentAdditionDialog::torrentAdditionDialog(GUI *parent, Bittorrent* _BTSession
 #if LIBTORRENT_VERSION_MINOR < 15
   addInSeed->setVisible(false);
 #endif
+  // Set Add button as default
+  OkButton->setDefault(true);
 }
 
 torrentAdditionDialog::~torrentAdditionDialog() {