Don't close already closed files in vio (not critical)

mysys/my_init.c

@@ -127,6 +127,7 @@ void my_end(int infoflag)
   FILE *info_file;
   if (!(info_file=DBUG_FILE))
     info_file=stderr;
+  DBUG_PRINT("info",("Shutting down"));
   if (infoflag & MY_CHECK_ERROR || info_file != stderr)
   {					/* Test if some file is left open */
     if (my_file_opened | my_stream_opened)

sql/mysqld.cc

@@ -1301,6 +1301,19 @@ void yyerror(const char *s)
 
 
 #ifndef EMBEDDED_LIBRARY
+/*
+  Close a connection
+
+  SYNOPSIS
+    close_connection()
+    thd		Thread handle
+    errcode	Error code to print to console
+    lock	1 if we have have to lock LOCK_thread_count
+
+  NOTES
+    For the connection that is doing shutdown, this is called twice
+*/
+
 void close_connection(THD *thd, uint errcode, bool lock)
 {
   st_vio *vio;

sql/sql_parse.cc

@@ -4562,7 +4562,6 @@ TABLE_LIST *st_select_lex::add_table_to_list(THD *thd,
   register TABLE_LIST *ptr;
   char *alias_str;
   DBUG_ENTER("add_table_to_list");
-  DBUG_PRINT("enter",("lock_option: %d", lock_type));
 
   if (!table)
     DBUG_RETURN(0);				// End of memory

vio/viosocket.c

@@ -203,9 +203,11 @@ int vio_close(Vio * vio)
 #endif
     r=CloseHandle(vio->hPipe);
   }
-  else if (vio->type != VIO_CLOSED)
+  else
 #endif /* __WIN__ */
+ if (vio->type != VIO_CLOSED)
   {
+    DBUG_ASSERT(vio->sd >= 0);
     if (shutdown(vio->sd,2))
       r= -1;
     if (closesocket(vio->sd))