Do not allow empty tables in EditTableForm

Do not allow the creation of a table without any columns as this would
lead to an SQL error.

src/EditTableForm.cpp

@@ -129,6 +129,8 @@ void editTableForm::checkInput()
     bool valid = true;
     if(ui->editTableName->text().isEmpty() || ui->editTableName->text().contains(" "))
         valid = false;
+    if(ui->treeWidget->topLevelItemCount() == 0)
+        valid = false;
     ui->buttonBox->button(QDialogButtonBox::Ok)->setEnabled(valid);
 }
 
@@ -167,6 +169,7 @@ void editTableForm::addField()
         tbitem->setText(1, dialog.field_type);
         modified = true;
         ui->treeWidget->addTopLevelItem(tbitem);
+        checkInput();
     }
 }
 
@@ -194,6 +197,8 @@ void editTableForm::removeField()
             QMessageBox::information(this, QApplication::applicationName(), tr("Sorry! This function is currently not implemented as SQLite does not support the deletion of columns yet."));
 //      }
     }
+
+    checkInput();
 }
 
 void editTableForm::fieldSelectionChanged()

src/EditTableForm.ui

@@ -270,6 +270,22 @@
     </hint>
    </hints>
   </connection>
+  <connection>
+   <sender>treeWidget</sender>
+   <signal>itemChanged(QTreeWidgetItem*,int)</signal>
+   <receiver>editTableForm</receiver>
+   <slot>checkInput()</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>138</x>
+     <y>197</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>412</x>
+     <y>135</y>
+    </hint>
+   </hints>
+  </connection>
  </connections>
  <slots>
   <slot>fieldSelectionChanged()</slot>