patch 8.1.2308: deleting text before zero-width textprop removes it

Problem:    Deleting text before zero-width textprop removes it.
Solution:   Keep zero-width textprop when deleting text.
diff --git a/src/version.c b/src/version.c
index a682517..00aa9e8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2308,
+/**/
     2307,
 /**/
     2306,