[bugfix] Only insert status pins if slice not empty (#4743)

Fix a little migration oopsie.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4743
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

internal/db/bundb/migrations/20260221171254_add_flags_column.go

@@ -183,10 +183,12 @@ func init() {
 			}
 
 			// Insert new pinned models.
-			if _, err := tx.NewInsert().
-				Model(&statusPins).
-				Exec(ctx); err != nil {
-				return gtserror.Newf("error inserting status pins: %w", err)
+			if len(statusPins) != 0 {
+				if _, err := tx.NewInsert().
+					Model(&statusPins).
+					Exec(ctx); err != nil {
+					return gtserror.Newf("error inserting status pins: %w", err)
+				}
 			}
 
 			// Increment updated total by ID count.