fix(gui): unsynchronized search index creation results in NullPointerException upon performing search (#429)

jadx-gui/src/main/java/jadx/gui/ui/SearchDialog.java

@@ -180,6 +180,7 @@ public class SearchDialog extends CommonSearchDialog {
 						.toList()
 						.toFlowable(), 1)
 				.observeOn(SwingSchedulers.edt())
+				.doOnError(e -> LOG.error("Error while searching: {}", e.getMessage(), e))
 				.subscribe(this::processSearchResults);
 	}
 

jadx-gui/src/main/java/jadx/gui/utils/search/CodeIndex.java

@@ -23,7 +23,7 @@ public class CodeIndex<T> implements SearchIndex<T> {
 	}
 
 	@Override
-	public void put(StringRef str, T value) {
+	public synchronized void put(StringRef str, T value) {
 		if (str == null || str.length() == 0) {
 			return;
 		}