Improve handling of invalid check-sat result in smtio.py

Signed-off-by: Clifford Wolf <clifford@clifford.at>

backends/smt2/smtio.py

@@ -646,12 +646,13 @@ class SmtIo:
                     sys.stderr.flush()
 
         result = self.read()
-        assert result in ["sat", "unsat"]
 
         if self.debug_file:
             print("(set-info :status %s)" % result, file=self.debug_file)
             print("(check-sat)", file=self.debug_file)
             self.debug_file.flush()
+
+        assert result in ["sat", "unsat"]
         return result
 
     def parse(self, stmt):