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>

libcockatrice_card/libcockatrice/card/database/parser/cockatrice_xml_4.cpp

@@ -18,6 +18,7 @@
 #include <QList>
 #include <QMap>
 #include <QMessageLogger>
+#include <QSaveFile>
 #include <QSharedPointer>
 #include <QStringList>
 #include <QStringView>
@@ -682,7 +683,7 @@ bool CockatriceXml4Parser::saveToFile(FormatRulesNameMap _formats,
                                       const QString &sourceUrl,
                                       const QString &sourceVersion)
 {
-    QFile file(fileName);
+    QSaveFile file(fileName);
     if (!file.open(QIODevice::WriteOnly)) {
         return false;
     }
@@ -730,5 +731,5 @@ bool CockatriceXml4Parser::saveToFile(FormatRulesNameMap _formats,
     xml.writeEndElement(); // cockatrice_carddatabase
     xml.writeEndDocument();
 
-    return true;
+    return !xml.hasError() && file.commit();
 }