Fix T87010: VSE: adding strips crashes in certain files

Caused by {rB571362642201} where versioning code for new sequencer tool
settings was only done for scenes already having sequencer scene->ed.

If scene->ed was not present, sequencer tool settings were never
initalized for this scene [if the VSE was then used later], leading to
crashes in some places.

Now just use the versioning code to initalize sequencer tool settings
for all scenes not having them yet.

Maniphest Tasks: T87010

Differential Revision: https://developer.blender.org/D10996

source/blender/blenloader/intern/versioning_290.c

@@ -1574,7 +1574,7 @@ void blo_do_versions_290(FileData *fd, Library *UNUSED(lib), Main *bmain)
     }
 
     LISTBASE_FOREACH (Scene *, scene, &bmain->scenes) {
-      if (scene->ed != NULL) {
+      if (scene->toolsettings->sequencer_tool_settings == NULL) {
         scene->toolsettings->sequencer_tool_settings = SEQ_tool_settings_init();
       }
     }