DBManager: merge PR2342 by medspx (fix #13650)

Author: brushtyler

python/plugins/db_manager/db_plugins/plugin.py

@@ -37,7 +37,8 @@ def __init__(self, e):
         else:
             msg = e
 
-        msg = unicode(val, 'utf-8', 'replace') # convert from utf8 and replace errors (if any)
+        if not isinstance(msg, unicode):
+             msg = unicode(msg, 'utf-8', 'replace') # convert from utf8 and replace errors (if any)
 
         self.msg = msg
         Exception.__init__(self, msg)