patch 8.2.0060: message test only runs with one encoding

Problem:    Message test only runs with one encoding. (Dominique Pelle)
Solution:   Run the test with "utf-8" and "latin1".  Fix underflow. (related
            to #5410)

Author: brammool

src/message.c

@@ -307,7 +307,8 @@ trunc_string(
     }
     else
     {
-	for (i = (int)STRLEN(s); len + (n = ptr2cells(s + i - 1)) <= room; --i)
+	for (i = (int)STRLEN(s);
+		   i - 1 >= 0 && len + (n = ptr2cells(s + i - 1)) <= room; --i)
 	    len += n;
     }
 

src/message_test.c

@@ -100,8 +100,14 @@ main(int argc, char **argv)
     params.argc = argc;
     params.argv = argv;
     common_init(&params);
+
+    set_option_value((char_u *)"encoding", 0, (char_u *)"utf-8", 0);
     init_chartab();
+    test_trunc_string();
 
+    set_option_value((char_u *)"encoding", 0, (char_u *)"latin1", 0);
+    init_chartab();
     test_trunc_string();
+
     return 0;
 }

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    60,
 /**/
     59,
 /**/