patch 8.0.1556: may not parse the t_RS response correctly

Problem:    May not parse the t_RS response correctly, resulting in wrong
            characters in the input stream.
Solution:   When the t_RS response is partly received wait for more
            characters.
diff --git a/src/version.c b/src/version.c
index 9a61422..e1f406a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -779,6 +779,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1556,
+/**/
     1555,
 /**/
     1554,