Preserve installed card databases when Oracle refresh fails (#7739)

* Preserve installed card databases when Oracle refresh fails

* Fix the Oracle refresh verdict and cover the parser write path

A background refresh that already installed cards.xml exited 1 when the
token save afterwards failed, so the client kept its old in-memory
database and reported the update as failed. Return the same verdict
main() already computes: a reject after the database was written is a
successful update.

Cover the writer Oracle actually uses: add a short-write death test for
CockatriceXml4Parser::saveToFile, which reverted to QFile would truncate
an installed database without any test noticing.

Route a failed background token download through reject() instead of a
modal box on a hidden wizard, which left the client waiting with no
timeout and blocked later updates. Test the first non-space byte in
place rather than copying the payload, and report an import refusal with
the importer's own message.

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

oracle/src/oraclewizard.cpp

@@ -1,6 +1,7 @@
 #include "oraclewizard.h"
 
 #include "client/settings/cache_settings.h"
+#include "database_writer.h"
 #include "main.h"
 #include "oracleimporter.h"
 #include "pages.h"
@@ -141,6 +142,13 @@ void OracleWizard::reject()
     }
 
     QWizard::reject();
+    // A hidden wizard does not close the application's last visible window.
+    // Stop background refreshes explicitly so the hosting client receives a verdict,
+    // using the same rule as main(): a reject after the database was written is still
+    // a successful update, only a reject that wrote nothing counts as a failure.
+    if (backgroundMode) {
+        QCoreApplication::exit(hasSavedDatabase() ? 0 : 1);
+    }
 }
 
 void OracleWizard::runInBackground()
@@ -212,17 +220,10 @@ void OracleWizard::disableButtons()
 
 bool OracleWizard::saveTokensToFile(const QString &fileName)
 {
-    QFile file(fileName);
-    if (!file.open(QIODevice::WriteOnly)) {
-        qDebug() << "File open (w) failed for" << fileName;
+    QString error;
+    if (!OracleDatabase::saveXml(fileName, tokensData, &error)) {
+        qWarning() << error;
         return false;
     }
-
-    if (file.write(tokensData) == -1) {
-        qDebug() << "File write (w) failed for" << fileName;
-        return false;
-    }
-
-    file.close();
     return true;
 }