qt: Enable and disable the Show and Remove buttons for requested payments history

based on whether any entry is selected.

src/qt/forms/receivecoinsdialog.ui

@@ -263,6 +263,9 @@
           <property name="text">
            <string>Show</string>
           </property>
+          <property name="enabled">
+           <bool>false</bool>
+          </property>
           <property name="icon">
            <iconset resource="../bitcoin.qrc">
             <normaloff>:/icons/edit</normaloff>:/icons/edit</iconset>
@@ -277,6 +280,9 @@
           <property name="text">
            <string>Remove</string>
           </property>
+          <property name="enabled">
+           <bool>false</bool>
+          </property>
           <property name="icon">
            <iconset resource="../bitcoin.qrc">
             <normaloff>:/icons/remove</normaloff>:/icons/remove</iconset>

src/qt/receivecoinsdialog.cpp

@@ -19,6 +19,7 @@
 #include <QMessageBox>
 #include <QTextDocument>
 #include <QScrollBar>
+#include <QItemSelection>
 
 ReceiveCoinsDialog::ReceiveCoinsDialog(QWidget *parent) :
     QDialog(parent),
@@ -77,6 +78,11 @@ void ReceiveCoinsDialog::setModel(WalletModel *model)
         ui->recentRequestsView->horizontalHeader()->resizeSection(RecentRequestsTableModel::Amount, 100);
 
         model->getRecentRequestsTableModel()->sort(RecentRequestsTableModel::Date, Qt::DescendingOrder);
+
+        connect(ui->recentRequestsView->selectionModel(),
+            SIGNAL(selectionChanged(QItemSelection, QItemSelection)),
+            this,
+            SLOT(on_recentRequestsView_selectionChanged(QItemSelection, QItemSelection)));
     }
 }
 
@@ -161,6 +167,15 @@ void ReceiveCoinsDialog::on_recentRequestsView_doubleClicked(const QModelIndex &
     dialog->show();
 }
 
+void ReceiveCoinsDialog::on_recentRequestsView_selectionChanged(const QItemSelection &selected,
+                                                                const QItemSelection &deselected)
+{
+    // Enable Show/Remove buttons only if anything is selected.
+    bool enable = !ui->recentRequestsView->selectionModel()->selectedRows().isEmpty();
+    ui->showRequestButton->setEnabled(enable);
+    ui->removeRequestButton->setEnabled(enable);
+}
+
 void ReceiveCoinsDialog::on_showRequestButton_clicked()
 {
     if(!model || !model->getRecentRequestsTableModel() || !ui->recentRequestsView->selectionModel())

src/qt/receivecoinsdialog.h

@@ -10,6 +10,7 @@
 #include <QMenu>
 #include <QPoint>
 #include <QVariant>
+#include <QItemSelection>
 
 namespace Ui {
     class ReceiveCoinsDialog;
@@ -51,6 +52,7 @@ private slots:
     void on_showRequestButton_clicked();
     void on_removeRequestButton_clicked();
     void on_recentRequestsView_doubleClicked(const QModelIndex &index);
+    void on_recentRequestsView_selectionChanged(const QItemSelection &, const QItemSelection &);
     void updateDisplayUnit();
     void showMenu(const QPoint &);
     void copyLabel();