VSE: fix versioning code to the new maximum zoom level (128)

Since we bumped the number of channels to 128, I forgot to doversion the
editors. So new files (new editors) would have this right, but not
existing files.

Fixup to: 8fecc2a852

source/blender/blenloader/intern/versioning_300.c

@@ -1520,5 +1520,21 @@ void blo_do_versions_300(FileData *fd, Library *UNUSED(lib), Main *bmain)
    */
   {
     /* Keep this block, even when empty. */
+
+    LISTBASE_FOREACH (bScreen *, screen, &bmain->screens) {
+      LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+        LISTBASE_FOREACH (SpaceLink *, sl, &area->spacedata) {
+          if (sl->spacetype == SPACE_SEQ) {
+            ListBase *regionbase = (sl == area->spacedata.first) ? &area->regionbase :
+                                                                   &sl->regionbase;
+            LISTBASE_FOREACH (ARegion *, region, regionbase) {
+              if (region->regiontype == RGN_TYPE_WINDOW) {
+                region->v2d.max[1] = MAXSEQ;
+              }
+            }
+          }
+        }
+      }
+    }
   }
 }