Subdl Provider: avoid raising exception on no results

ProviderError is raised when the movie or the TVShow is not found,
causing Bazarr to throttle the provider instead of returning an empty
list.

custom_libs/subliminal_patch/providers/subdl.py

@@ -181,7 +181,8 @@ class SubdlProvider(ProviderRetryMixin, Provider):
         result = res.json()
 
         if ('success' in result and not result['success']) or ('status' in result and not result['status']):
-            raise ProviderError(result['error'])
+            logger.debug(result["error"])
+            return []
 
         logger.debug(f"Query returned {len(result['subtitles'])} subtitles")