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/oracleimporter.h

@@ -198,6 +198,11 @@ private:
      * the whole import (or racing it).
      */
     QAtomicInt importCancelled;
+    bool importSuccessful = false;
+    QString importError;
+
+    // Discard the incomplete in-memory database; the installed file is untouched.
+    int failImport(const QString &message);
 
     /**
      * The ISO-639 language code whose foreignData is imported; "en" by default.
@@ -278,7 +283,24 @@ public:
      * the wizard can hand over its decompressed buffer without copying it.
      */
     bool readSetsFromByteArray(QByteArray data);
+    // Returns the complete selected-set count on success, zero on failure or cancellation.
     int startImport();
+    bool hasSuccessfulImport() const
+    {
+        return importSuccessful;
+    }
+    const QString &getImportError() const
+    {
+        return importError;
+    }
+    // Call on the owning thread before scheduling a worker, so a cancellation
+    // arriving before that worker starts is not lost.
+    void prepareImport()
+    {
+        importCancelled.storeRelease(0);
+        importSuccessful = false;
+        importError.clear();
+    }
     /**
      * @brief Requests an in-flight startImport() to stop at the next set boundary.
      *