patch 8.1.2349: :lockvar and :unlockvar cannot be followed by "| endif"

Problem:    :lockvar and :unlockvar cannot be followed by "| endif".
Solution:   Check for following commands. (closes #5269)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 576a756..ed7512f 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2384,6 +2384,7 @@
 	    case CMD_leftabove:
 	    case CMD_let:
 	    case CMD_lockmarks:
+	    case CMD_lockvar:
 	    case CMD_lua:
 	    case CMD_match:
 	    case CMD_mzscheme:
@@ -2408,6 +2409,7 @@
 	    case CMD_tilde:
 	    case CMD_topleft:
 	    case CMD_unlet:
+	    case CMD_unlockvar:
 	    case CMD_verbose:
 	    case CMD_vertical:
 	    case CMD_wincmd: