Check whether active transaction still exists before rollback

If transaction has become broken during commit its rollback leads to
new exception which will overwrite the original one.
Check for active transaction should work because on exception within
driver.CommitTransaction() active transaction is set to NULL.

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Upgrade/UpgradingDomainBuilder.cs

@@ -172,7 +172,13 @@ private void CompleteUpgradeTransaction()
         driver.CommitTransaction(null, connection);
       }
       catch {
-        driver.RollbackTransaction(null, connection);
+        // If transaction has become broken during commit its rollback leads to new exception
+        // which will overwrite the original one.
+        // Check for active transaction should work because on exception within 
+        // driver.Commit it is set to NULL.
+        if (connection.ActiveTransaction != null) {
+          driver.RollbackTransaction(null, connection);
+        }
         throw;
       }
     }
@@ -190,7 +196,13 @@ private async ValueTask CompleteUpgradeTransactionAsync(CancellationToken token)
         await driver.CommitTransactionAsync(null, connection, token);
       }
       catch {
-        await driver.RollbackTransactionAsync(null, connection, token);
+        // If transaction has become broken during commit its rollback leads to new exception
+        // which will overwrite the original one.
+        // Check for active transaction should work because on exception within 
+        // driver.Commit it is set to NULL.
+        if (connection.ActiveTransaction != null) {
+          await driver.RollbackTransactionAsync(null, connection, token);
+        }
         throw;
       }
     }