Don't call mysql_close() when InactiveDestroy is set

Without this change, the END block of DBI would call disconnect_all()
and that would call mysql_close() on all open connections. This is bad
because forks would destroy their parent's context on exit as shown in
the example for AutoInactiveDestroy in the DBI docs.

This example fails with "DBD::MariaDB::db do failed: Lost connection to
MySQL server during query" without this fix:

  $dbh->{'AutoInactiveDestroy'} = 1;
  if (my $pid = fork()) {
    waitpid($pid, 0);
    $dbh->do('SELECT 1');
  } else {
    exit(0);
  }

Author: rovo89

dbdimp.c

@@ -2956,11 +2956,12 @@ mariadb_db_rollback(SV* dbh, imp_dbh_t* imp_dbh) {
   return 1;
 }
 
-static void mariadb_dr_close_mysql(pTHX_ imp_drh_t *imp_drh, MYSQL *pmysql)
+static void mariadb_dr_close_mysql(pTHX_ imp_drh_t *imp_drh, MYSQL *pmysql, bool actually_close)
 {
   if (pmysql)
   {
-    mysql_close(pmysql);
+    if (actually_close)
+      mysql_close(pmysql);
     imp_drh->instances--;
   }
   if (imp_drh->instances == 0)
@@ -3021,7 +3022,7 @@ static void mariadb_db_close_mysql(pTHX_ imp_drh_t *imp_drh, imp_dbh_t *imp_dbh)
 
   if (imp_dbh->pmysql)
   {
-    mariadb_dr_close_mysql(aTHX_ imp_drh, imp_dbh->pmysql);
+    mariadb_dr_close_mysql(aTHX_ imp_drh, imp_dbh->pmysql, DBIc_ACTIVE(imp_dbh));
     imp_dbh->pmysql = NULL;
     svp = hv_fetchs((HV*)DBIc_MY_H(imp_dbh), "ChildHandles", FALSE);
     if (svp && *svp)
@@ -3059,6 +3060,8 @@ static void mariadb_db_close_mysql(pTHX_ imp_drh_t *imp_drh, imp_dbh_t *imp_dbh)
       }
     }
   }
+
+  DBIc_ACTIVE_off(imp_dbh);
 }
 
 /*
@@ -3112,7 +3115,7 @@ int mariadb_dr_discon_all (SV *drh, imp_drh_t *imp_drh) {
 
   while ((entry = imp_drh->taken_pmysqls))
   {
-    mariadb_dr_close_mysql(aTHX_ imp_drh, (MYSQL *)entry->data);
+    mariadb_dr_close_mysql(aTHX_ imp_drh, (MYSQL *)entry->data, TRUE);
     mariadb_list_remove(imp_drh->taken_pmysqls, entry);
   }