### Describe the issue
In Bitcoin QT, under the Transactions tab when right clicking on the transaction the context menu shows more option then it can always handle.

### Can you reliably reproduce the issue?
Yes.

#### If so, please list the steps to reproduce below:  
0. Open QT.  
1. Make an incoming transaction without label.  
2. Go to the Transactions tab.  
3. Rigth click on a transaction and select "Copy label".  

### Actual behaviour
The clipboard will be empty.  

### Expected behaviour
Copies the label. (What does not exist, of course.)

### What version of bitcoin-core are you using?
v0.13.1, Ubuntu PPA.  

### Any extra information that might be useful in the debugging process.
This behaviour is more problematic in edge cases.  
Like when you send funds with JoinMarket. In this case for example the "Copy address" option does not work.  

### Suggestion
I think when something cannot be copied that should not be present in the context menu in the first place.  
  
![](http://i.imgur.com/hLfAgeF.png)
is selected.
       @param[in] column  Data column to extract from the model
       @param[in] role    Data role to extract from the model
       @see  TransactionView::copyLabel, TransactionView::copyAmount, TransactionView::copyAddress
     */
    void copyEntryData(QAbstractItemView *view, int column, int role=Qt::EditRole);
    /** Return a field of the currently selected entry as a QString. Does nothing if nothing
        is selected.
       @param[in] column  Data column to extract from the model
       @see  TransactionView::copyLabel, TransactionView::copyAmount, TransactionView::copyAddress
     */
    QList<QModelIndex> getEntryData(QAbstractItemView *view, int column);
    void setClipboard(const QString& str);
    /**
     * Determine default data directory for operating system.
     */
    QString getDefaultDataDirectory();
    /** Get save filename, mimics QFileDialog::getSaveFileName, except that it appends a default suffix
        when no suffix is provided by the user.
      @param[in] parent  Parent window (or 0)
      @param[in] caption Window caption (or empty, for default)
      @param[in] dir     Starting directory (or empty, to default to documents directory)
      @param[in] filter  Filter specification such as "Comma Separated Files (*.csv)"
      @param[out] selectedSuffixOut  Pointer to return the suffix (file type) that was selected (or 0).
                  Can be useful when choosing the save file format based on suffix.
     */
    QString getSaveFileName(QWidget *parent, const QString &caption, const QString &dir,
        const QString &filter,
        QString *selectedSuffixOut);
    /** Get open filename, convenience wrapper for QFileDialog::getOpenFileName.