patch 8.1.2302: :lockmarks does not work for '[ and ']

Problem:    :lockmarks does not work for '[ and '].
Solution:   save and restore '[ and '] marks. (James McCoy, closes #5222)
diff --git a/src/indent.c b/src/indent.c
index 755c3a9..8d574c8 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1001,9 +1001,12 @@
 	smsg(NGETTEXT("%ld line indented ",
 						 "%ld lines indented ", i), i);
     }
-    // set '[ and '] marks
-    curbuf->b_op_start = oap->start;
-    curbuf->b_op_end = oap->end;
+    if (!cmdmod.lockmarks)
+    {
+	// set '[ and '] marks
+	curbuf->b_op_start = oap->start;
+	curbuf->b_op_end = oap->end;
+    }
 }
 #endif // defined(FEAT_LISP) || defined(FEAT_CINDENT)