Fix potential assert on itersel selection restoration

We cannot guarantee after an itersel that selections are going to
still be in ascending order, but we were calling a SelectionList
constructor that was assuming this was the case.

src/commands.cc

@@ -1662,16 +1662,16 @@ void context_wrap(const ParametersParser& parser, Context& context, Func func)
 
                 update_selections(new_sels, main, c.buffer(), timestamp);
                 timestamp = c.buffer().timestamp();
+                if (&sel == &sels.main())
+                    main = new_sels.size() + c.selections().main_index();
+
                 for (auto& sel : c.selections())
                     new_sels.push_back(sel);
             }
         }
 
         if (not draft)
-        {
-            c.selections_write_only() = SelectionList(c.buffer(), std::move(new_sels));
-            c.selections().sort_and_merge_overlapping();
-        }
+            c.selections_write_only().set(std::move(new_sels), main);
     }
     else
     {

test/regression/0-assert-on-itersel/cmd

@@ -0,0 +1 @@
+:exec -itersel jj<ret>

test/regression/0-assert-on-itersel/in

@@ -0,0 +1,3 @@
+line %(1)
+%(l)ine 2
+line 3

test/regression/0-assert-on-itersel/selections

@@ -0,0 +1 @@
+l:3