minidb: Fix encoding issue (bug 1088)

Make sure that utf-8 strings are converted
to unicode before sending to the database.

src/gpodder/minidb.py

@@ -85,8 +85,10 @@ def _register(self, class_):
                         ', '.join('%s TEXT'%s for s in slots)))
 
     def convert(self, v):
-        if isinstance(v, str) or isinstance(v, unicode):
+        if isinstance(v, unicode):
             return v
+        elif isinstance(v, str):
+            return v.decode('utf-8')
         else:
             return str(v)