Alter default and document icon setting

Previous default value prevented the preceding commit from working
(by default), oops.

doc/geany.txt

@@ -2498,6 +2498,8 @@ msgwin_messages_visible           Whether to show the Messages tab in the    tru
                                   Messages Window
 msgwin_scribble_visible           Whether to show the Scribble tab in the    true        immediately
                                   Messages Window
+use_geany_icon                    Whether to use the Geany icon on the       false       on restart
+                                  window instead of the theme's icon
 ================================  =========================================  ==========  ===========
 
 By default, statusbar_template is empty. This tells Geany to use its

src/keyfile.c

@@ -243,7 +243,7 @@ static void init_pref_groups(void)
     
     /* use the Geany icon instead of the theme */
     stash_group_add_boolean(group, &main_use_geany_icon,
-        "use_geany_icon", TRUE);
+        "use_geany_icon", FALSE);
 }