MainWindow: Checker: Add worker.

src/Checker/Checker.py

@@ -40,7 +40,7 @@ class STATUS(Enum):
 
     def __or__(self, y):
         v = [self, y]
-        res = self.OK
+        r = self.OK
 
         if self.UNKNOWN in v:
             r = self.UNKNOWN
@@ -60,6 +60,9 @@ class AbstractModelChecker(object):
         self._solver = "study"
         self._modules = Modules.NONE
 
+        self.reset()
+
+    def reset(self):
         self._status = STATUS.UNKNOWN
         self._summary = "Unknown"