[geary/wip/728002-webkit2] Fix some more issues on earlier GTK versions.

[Michael Gratton <mjog src gnome org>]

commit 6e9a37efa4c989a128c2e1531cce9067ae96ea2d
Author: Michael James Gratton <mike vee net>
Date:   Mon Jan 30 15:39:47 2017 +1100

    Fix some more issues on earlier GTK versions.
    
    * src/client/composer/composer-link-popover.vala:
      Gtk.Popover::set_default_widget is only available in GTK+ 3.18,
      Gtk.Widget::set_tooltop_text param can't be null in earlier GTK vala
      bindings.

 src/client/composer/composer-link-popover.vala |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/client/composer/composer-link-popover.vala b/src/client/composer/composer-link-popover.vala
index 538801a..26fb86a 100644
--- a/src/client/composer/composer-link-popover.vala
+++ b/src/client/composer/composer-link-popover.vala
@@ -72,7 +72,8 @@ public class ComposerLinkPopover : Gtk.Popover {
 
 
     public ComposerLinkPopover(Type type) {
-        set_default_widget(this.url);
+        // GTK_ 3.18: Re-enable this
+        //set_default_widget(this.url);
         set_focus_child(this.url);
         switch (type) {
         case Type.NEW_LINK:
@@ -159,7 +160,7 @@ public class ComposerLinkPopover : Gtk.Popover {
             style.remove_class(Gtk.STYLE_CLASS_ERROR);
             style.remove_class(Gtk.STYLE_CLASS_WARNING);
             this.url.set_icon_from_icon_name(pos, null);
-            this.url.set_tooltip_text(null);
+            this.url.set_tooltip_text("");
         }
 
         link_changed(url, is_valid && is_nominal);