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.

src/version.c

@@ -778,6 +778,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1556,
 /**/
     1555,
 /**/