Segfault when clearing entry

[JFronny]

This is probably a bug in GTK and not in this library, but I found it here and know nothing about C, so I am reporting it here. When setting the content of a org.gnome.gtk.Entry, I usually use the setText convenience method provided by Editable. This works for strings containing one or more characters, but causes a segfault for empty strings ("") or null. While the latter is expected, the former seems weird. I know I can work around this using the buffer obtainable via entry.getBuffer(), but that removes the point of having a convenience method in the first place.

Code (using GTK4 4.12.0, GLib 2.76.4, java-gi 0.6.1 and OpenJDK 20.0.2)

```java package io.gitlab.jfronny; import org.gnome.gtk.*; import org.gnome.gio.ApplicationFlags; public class ExampleApp { public static void main(String[] args) { new ExampleApp().run(args); } private final Application app; public ExampleApp() { app = new Application("io.gitlab.jfronny.ExampleApp", ApplicationFlags.DEFAULT_FLAGS); app.onActivate(this::activate); } public void run(String[] args) { app.run(args); } public void activate() { var window = new ApplicationWindow(app); window.setTitle("GTK Example"); window.setDefaultSize(300, 200); var box = new Box(Orientation.VERTICAL, 0); box.setHalign(Align.CENTER); box.setValign(Align.CENTER); var entry = new Entry(); entry.setText("This is some text"); box.append(entry); var button1 = Button.newWithLabel("Test Button 1"); // This works button1.onClicked(() -> entry.setText("This is different text")); box.append(button1); var button2 = Button.newWithLabel("Test Button 2"); // This doesn't work button2.onClicked(() -> entry.setText(null)); box.append(button2); var button3 = Button.newWithLabel("Test Button 3"); // This doesn't work button3.onClicked(() -> entry.setText("")); box.append(button3); var button4 = Button.newWithLabel("Test Button 4"); // This works button4.onClicked(() -> clear(entry.getBuffer())); box.append(button4); window.setChild(box); window.present(); } private void clear(EntryBuffer buffer) { buffer.deleteText(0, buffer.getLength()); } } ```

[jwharm]

There's a bug in java-gi version 0.6.1 when marshaling empty strings. The empty string was marshaled to a null pointer. It is already resolved in the main branch (with this commit).