Twig settings are not available while indexing

Instead of throwing an exception, handle dumb mode and explain it to the user.

Closes #1222

Author: ruudk

src/main/java/fr/adrienbrault/idea/symfony2plugin/ui/TwigSettingsForm.java

@@ -2,7 +2,9 @@
 
 import com.intellij.openapi.options.Configurable;
 import com.intellij.openapi.options.ConfigurationException;
+import com.intellij.openapi.project.DumbService;
 import com.intellij.openapi.project.Project;
+import com.intellij.openapi.ui.DialogWrapper;
 import com.intellij.ui.ToolbarDecorator;
 import com.intellij.ui.table.TableView;
 import com.intellij.util.ui.ColumnInfo;
@@ -50,6 +52,12 @@ private void attachItems() {
             return;
         }
 
+        if (DumbService.getInstance(project).isDumb()) {
+            this.tableView.getEmptyText().setText("Not available while indexing. Please re-open this screen when ready.");
+
+            return;
+        }
+
         List<TwigPath> sortableLookupItems = new ArrayList<>(TwigUtil.getTwigNamespaces(this.project, true));
         Collections.sort(sortableLookupItems);