MDEV-3885 - connection suicide via mysql_kill() causes assertion in server

Assertion happened because sql_kill did not set OK status in diagnostic area
in the case of connection suicide (id to kill == thd->thread_id), issued 
via  COM_PROCESS_KILL , e.g using mysql_kill()

This patch ensures that diagnostic area is initialized in this specific case.

sql/sql_parse.cc

@@ -6717,7 +6717,7 @@ void sql_kill(THD *thd, ulong id, killed_state state)
   uint error;
   if (!(error= kill_one_thread(thd, id, state)))
   {
-    if (! thd->killed)
+    if ((!thd->killed) || (thd->thread_id == id))
       my_ok(thd);
   }
   else

tests/mysql_client_test.c

@@ -18554,6 +18554,22 @@ static void test_progress_reporting()
   mysql_close(conn);
 }
 
+/**
+  MDEV-3885 - connection suicide via mysql_kill() causes assertion in server
+*/
+
+static void test_mdev3885() 
+{
+  int rc;
+  MYSQL *conn;
+
+  myheader("test_mdev3885");
+  conn= client_connect(0, MYSQL_PROTOCOL_TCP, 0);
+  rc= mysql_kill(conn, mysql_thread_id(conn));
+  DIE_UNLESS(rc == 0);
+  mysql_close(conn);
+}
+
 
 /**
   Bug#57058 SERVER_QUERY_WAS_SLOW not wired up.
@@ -19056,6 +19072,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bug58036", test_bug58036 },
   { "test_bug57058", test_bug57058 },
   { "test_bug56976", test_bug56976 },
+  { "test_mdev3855", test_mdev3885 },
   { "test_bug11766854", test_bug11766854 },
   { "test_bug12337762", test_bug12337762 },
   { "test_progress_reporting", test_progress_reporting },