Qt: Improve clarity of unknown dump hashes

src/duckstation-qt/gamesummarywidget.cpp

@@ -593,6 +593,12 @@ void GameSummaryWidget::onComputeHashClicked()
       text = tr("Revision: %1").arg(found_revision.empty() ? tr("N/A") : QString::fromStdString(found_revision));
 
     if (found_serial != m_ui.serial->text().toStdString())
+    {
+      if (found_serial.empty())
+      {
+        text = tr("No known dump found that matches this hash.");
+      }
+      else
       {
         const QString mismatch_str =
           tr("Serial Mismatch: %1 vs %2").arg(QString::fromStdString(found_serial)).arg(m_ui.serial->text());
@@ -601,6 +607,7 @@ void GameSummaryWidget::onComputeHashClicked()
         else
           text = mismatch_str;
       }
+    }
 
     setRevisionText(text);
   }