patch 8.1.1342: using freed memory when joining line with text property

Problem:    Using freed memory when joining line with text property.
Solution:   Use already computed length.

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1342,
 /**/
     1341,
 /**/