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/bufwrite.c b/src/bufwrite.c
index 13091a3..8393df1 100644
--- a/src/bufwrite.c
+++ b/src/bufwrite.c
@@ -683,6 +683,8 @@
     context_sha256_T sha_ctx;
 #endif
     unsigned int    bkc = get_bkc_value(buf);
+    pos_T	    orig_start = buf->b_op_start;
+    pos_T	    orig_end = buf->b_op_end;
 
     if (fname == NULL || *fname == NUL)	// safety check
 	return FAIL;
@@ -875,6 +877,13 @@
 #endif
 				       )
 	{
+	    if (buf != NULL && cmdmod.lockmarks)
+	    {
+		// restore the original '[ and '] positions
+		buf->b_op_start = orig_start;
+		buf->b_op_end = orig_end;
+	    }
+
 	    --no_wait_return;
 	    msg_scroll = msg_save;
 	    if (nofile_err)
@@ -952,6 +961,13 @@
 	    fname = buf->b_sfname;
     }
 
+    if (cmdmod.lockmarks)
+    {
+	// restore the original '[ and '] positions
+	buf->b_op_start = orig_start;
+	buf->b_op_end = orig_end;
+    }
+
 #ifdef FEAT_NETBEANS_INTG
     if (netbeans_active() && isNetbeansBuffer(buf))
     {