Fixes terminal emulator misbehaviour as outlined in https://gitlab.gnome.org/GNOME/gtk/issues/1316, which was introduced in 49b17e6c. The original commit cleared preedit text by setting it to an empty string, which still counted as existing preedit. The fix sets preedit string to null, which is correctly understood as not present.
There may be situations where this might get called while the
currently focused context just went away (eg. after setting the
text widget unsensitive).
Closes: #1317
This fixes a potential leak of a PangoAttrList that is set when chaining
up to the parent get_preedit_string(). We check to see if the attr list
was created and reuse it instead of leaking the previous value.
If the parent get_preedit_string implementation returns a nonnull
zero-length string, then we ignore it, which is almost fine. We have to
free it, though.
Fixes#1174
When generating introspection data, we instantiate types without
calling gtk_init, so make sure that extension points are registered
before the type is trying to implement them.
