Fix T98715: Crash drag-dropping collection from outliner to ID property

The value of disabled buttons shouldn't be changed through dropping onto
it. Check for the disabled state in the drop operator poll, so the
dragging code will change the cursor to show that dropping isn't
possible at the given cursor location.

source/blender/editors/interface/interface_handlers.c

@@ -2945,6 +2945,9 @@ void ui_but_text_password_hide(char password_str[UI_MAX_PASSWORD_STR],
 
 void ui_but_set_string_interactive(bContext *C, uiBut *but, const char *value)
 {
+  /* Caller should check. */
+  BLI_assert((but->flag & UI_BUT_DISABLED) == 0);
+
   button_activate_state(C, but, BUTTON_STATE_TEXT_EDITING);
   ui_textedit_string_set(but, but->active, value);
 

source/blender/editors/interface/interface_ops.c

@@ -1942,6 +1942,24 @@ static void UI_OT_drop_color(wmOperatorType *ot)
 /** \name Drop Name Operator
  * \{ */
 
+static bool drop_name_poll(bContext *C)
+{
+  if (!ED_operator_regionactive(C)) {
+    return false;
+  }
+
+  const uiBut *but = UI_but_active_drop_name_button(C);
+  if (!but) {
+    return false;
+  }
+
+  if (but->flag & UI_BUT_DISABLED) {
+    return false;
+  }
+
+  return true;
+}
+
 static int drop_name_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
 {
   uiBut *but = UI_but_active_drop_name_button(C);
@@ -1961,7 +1979,7 @@ static void UI_OT_drop_name(wmOperatorType *ot)
   ot->idname = "UI_OT_drop_name";
   ot->description = "Drop name to button";
 
-  ot->poll = ED_operator_regionactive;
+  ot->poll = drop_name_poll;
   ot->invoke = drop_name_invoke;
   ot->flag = OPTYPE_UNDO | OPTYPE_INTERNAL;