[gnumeric] SheetConditions: fix signal unhokking problem.

[Morten Welinder <mortenw src gnome org>]

commit 7cab38c6a6936d44f9e2269c0cdfda9f3c36030f
Author: Morten Welinder <terra gnome org>
Date:   Sun Aug 30 13:50:24 2020 -0400

    SheetConditions: fix signal unhokking problem.
    
    The sheet can outlive the workbook if someone holds on to a ref.  Survive
    that situation with a weak ref to the workbook.

 src/sheet-conditions.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)
---
diff --git a/src/sheet-conditions.c b/src/sheet-conditions.c
index 5ee98a676..f28ce13c0 100644
--- a/src/sheet-conditions.c
+++ b/src/sheet-conditions.c
@@ -104,6 +104,7 @@ struct GnmSheetConditionsData_ {
        GHashTable *linked_conditions;
 
        gulong sig_being_loaded;
+       gpointer sig_being_loaded_object;
 };
 
 static void update_group (CSGroup *g);
@@ -155,12 +156,17 @@ sheet_conditions_init (Sheet *sheet)
                ((GHashFunc)gnm_style_conditions_hash,
                 (GCompareFunc)sc_equal);
 
-       cd->sig_being_loaded = sheet->workbook
-               ? g_signal_connect_swapped (G_OBJECT (sheet->workbook),
-                                           "notify::being-loaded",
-                                           G_CALLBACK (cb_being_loaded),
-                                           sheet)
-               : 0; // a preview grid sheet
+       cd->sig_being_loaded_object = sheet->workbook;
+       if (cd->sig_being_loaded_object) {
+               cd->sig_being_loaded =
+                       g_signal_connect_swapped (G_OBJECT (cd->sig_being_loaded_object),
+                                                 "notify::being-loaded",
+                                                 G_CALLBACK (cb_being_loaded),
+                                                 sheet);
+               // We can't grab a ref to the workbook as that would introduce a ref loop.
+               g_object_add_weak_pointer (cd->sig_being_loaded_object,
+                                          &cd->sig_being_loaded_object);
+       }
 }
 
 
@@ -169,9 +175,12 @@ sheet_conditions_uninit (Sheet *sheet)
 {
        GnmSheetConditionsData *cd = sheet->conditions;
 
-       if (cd->sig_being_loaded) {
-               g_signal_handler_disconnect (sheet->workbook, cd->sig_being_loaded);
+       if (cd->sig_being_loaded_object) {
+               g_signal_handler_disconnect (cd->sig_being_loaded_object, cd->sig_being_loaded);
+               g_object_remove_weak_pointer (cd->sig_being_loaded_object,
+                                             &cd->sig_being_loaded_object);
                cd->sig_being_loaded = 0;
+               cd->sig_being_loaded_object = NULL;
        }
 
        if (g_hash_table_size (cd->groups) > 0)