change error reporting for full backup remote verification (#5004)

Before the change, it could happen that when the postbackup test
was finding problems in the backend, the job would be reported
as having completed successfully, the found problems being displayed
only in the complete log. After the change, an error is logged
that cause the job to be failed.
To repro, the following procedure can be used in a test backup:
change a hash for a block in the block table database and run a backup having set
--full-remote-verification and --full-block-verification to true and
--backup-test-percentage to 100.

Duplicati/Library/Main/Operation/TestHandler.cs

@@ -189,6 +189,15 @@ namespace Duplicati.Library.Main.Operation
             }
 
             m_results.EndTime = DateTime.UtcNow;
+            var filtered = from n in m_results.Verifications where n.Value.Any() select n;
+            if (!filtered.Any())
+            {
+                Logging.Log.WriteInformationMessage(LOGTAG, "Test results", "Successfully verified {0} remote files", m_results.VerificationsActualLength);
+            }
+            else
+            {
+                Logging.Log.WriteErrorMessage(LOGTAG, "Test results", null,  "Verified {0} remote files with {1} problem(s)", m_results.VerificationsActualLength, filtered.Count());
+            }
         }
 
         /// <summary>