Decode msg obtained from QtMsgHandler

Use utf-8 as a guess here, but make sure encoding errors
don't prevent a message from being displayed

Author: nicoddemus

pytestqt/plugin.py

@@ -487,6 +487,8 @@ def handle(self, msg_type, msg):
         Method to be installed using qInstallMsgHandler, stores each message
         into the `messages` attribute.
         """
+        if type(msg) is bytes:
+            msg = msg.decode('utf-8', errors='replace')
         self.messages.append(self.Message(msg_type, msg))
 
     @classmethod