pamhyr: Fix #20 study reload whene study is not saved on a file.

src/config.py

@@ -316,6 +316,9 @@ class Config(SQL):
         self.commit()
 
     def set_last_study(self, filename):
+        if filename is None:
+            return
+
         self.last_study = filename
         self.close_correctly = False
         self.execute(