debugger: let 'attach to running process' dialog activate the 'ok' button if

there's only one choice after filtering

src/plugins/debugger/debuggerdialogs.h

@@ -95,6 +95,7 @@ private slots:
     void rebuildProcessList();
     void procSelected(const QModelIndex &);
     void pidChanged(const QString &);
+    void setFilterString(const QString &filter);
 
 private:
     inline QPushButton *okButton() const;