patch 8.1.0551: expression evaluation may repeat an error message

Problem:    Expression evaluation may repeat an error message. (Jason
            Franklin)
Solution:   Check for the value of did_emsg when giving an error
            for the :execute command.

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    551,
 /**/
     550,
 /**/