patch 8.1.1387: calling prop_add() in an empty buffer doesn't work

Problem:    Calling prop_add() in an empty buffer doesn't work. (Dominique
            Pelle)
Solution:   Open the memline before adding a text property. (closes #4412)
diff --git a/src/version.c b/src/version.c
index 3653b9b..ac1c67a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1387,
+/**/
     1386,
 /**/
     1385,