bugfix: reader read also previous files

src/gui_qt/io/filereaders.py

@@ -41,6 +41,9 @@ class QFileReader(QtCore.QObject):
         return self.readfiles(files)
 
     def readfiles(self, fname: list[str] | str) -> list:
+        # clear old data
+        self.data = []
+
         if not isinstance(fname, list):
             fname = [fname]