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)

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1387,
 /**/
     1386,
 /**/