Fix mne_browse segfault: dangling QFile in openFiffRawData

QFile rawFile was local to openFiffRawData() but FiffRawData's
internal FiffStream held a pointer to it. After the function returned,
read_raw_segment() called isOpen() on the destroyed QFile → SIGSEGV.

Fix: use the persistent member m_qFileRaw directly.

Author: chdinh

src/applications/mne_browse/Windows/mainwindow.cpp

@@ -1224,8 +1224,11 @@ bool MainWindow::openFiffRawData(FIFFLIB::FiffRawData& raw, const QString& featu
         statusBar()->showMessage(tr("Load a raw FIF file before using %1.").arg(label), 5000);
         return false;
     }
-    QFile rawFile(m_qFileRaw.fileName());
-    raw = FIFFLIB::FiffRawData(rawFile);
+    // Re-open the member QFile so FiffRawData's internal FiffStream holds a
+    // valid QIODevice* that outlives this function call.
+    if (m_qFileRaw.isOpen())
+        m_qFileRaw.close();
+    raw = FIFFLIB::FiffRawData(m_qFileRaw);
 #endif
 
     if (raw.isEmpty()) {