[gtk/constraint-guide-3] constraint solver: Fix repeat suggestions

[Matthias Clasen <matthiasc src gnome org>]

commit 49897bdce859174268d16d5913368c41e0ee3aea
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jun 28 16:59:39 2019 +0000

    constraint solver: Fix repeat suggestions
    
    We were not storing the previous value, causing
    the first two suggestions to work, but not later
    ones.
    
    Fixes the test added in the previous commit.

 gtk/gtkconstraintsolver.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkconstraintsolver.c b/gtk/gtkconstraintsolver.c
index 1516a08675..e29c7665fc 100644
--- a/gtk/gtkconstraintsolver.c
+++ b/gtk/gtkconstraintsolver.c
@@ -1973,6 +1973,7 @@ gtk_constraint_solver_suggest_value (GtkConstraintSolver *self,
                                      double value)
 {
   EditInfo *ei = g_hash_table_lookup (self->edit_var_map, variable);
+  double delta;
   if (ei == NULL)
     {
       g_critical ("Suggesting value '%g' but variable %p is not editable",
@@ -1988,9 +1989,10 @@ gtk_constraint_solver_suggest_value (GtkConstraintSolver *self,
       return;
     }
 
-  ei->prev_constant = value - ei->prev_constant;
+  delta = value - ei->prev_constant;
+  ei->prev_constant = value;
 
-  gtk_constraint_solver_delta_edit_constant (self, ei->prev_constant, ei->eplus, ei->eminus);
+  gtk_constraint_solver_delta_edit_constant (self, delta, ei->eplus, ei->eminus);
 }
 
 /*< private >