Fixing error where casting .lower on non string

couchpotato/core/media/movie/providers/info/omdbapi.py

@@ -88,6 +88,7 @@ class OMDBAPI(MovieProvider):
 
             tmp_movie = movie.copy()
             for key in tmp_movie:
+                if type(tmp_movie.get(key)) is string:
                     if tmp_movie.get(key).lower() == 'n/a':
                         del movie[key]