patch 7.4.2223
Problem:    Buffer overflow when using latin1 character with feedkeys().
Solution:   Check for an illegal character.  Add a test.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index cc38d94..b427ecf 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -11166,7 +11166,7 @@
 		break;
 	    }
 	    --charidx;
-	    byteidx += mb_cptr2len(str + byteidx);
+	    byteidx += MB_CPTR2LEN(str + byteidx);
 	}
     }
 #else
@@ -11326,7 +11326,7 @@
 	if (nchar > 0)
 	    while (nchar > 0 && nbyte < slen)
 	    {
-		nbyte += mb_cptr2len(p + nbyte);
+		nbyte += MB_CPTR2LEN(p + nbyte);
 		--nchar;
 	    }
 	else
@@ -11341,7 +11341,7 @@
 		if (off < 0)
 		    len += 1;
 		else
-		    len += mb_cptr2len(p + off);
+		    len += MB_CPTR2LEN(p + off);
 		--charlen;
 	    }
 	}