improve find() for downloaders and postprocessors

gallery_dl/downloader/__init__.py

@@ -30,9 +30,10 @@ def find(scheme):
     if scheme in modules:  # prevent unwanted imports
         try:
             module = importlib.import_module("." + scheme, __package__)
-            klass = module.__downloader__
         except ImportError:
             pass
+        else:
+            klass = module.__downloader__
 
     if scheme == "http":
         _cache["http"] = _cache["https"] = klass

gallery_dl/postprocessor/__init__.py

@@ -28,15 +28,18 @@ def find(name):
     try:
         return _cache[name]
     except KeyError:
-        klass = None
+        pass
+
+    klass = None
+    if name in modules:  # prevent unwanted imports
         try:
-            if name in modules:  # prevent unwanted imports
-                module = importlib.import_module("." + name, __package__)
-                klass = module.__postprocessor__
-        except (ImportError, AttributeError, TypeError):
+            module = importlib.import_module("." + name, __package__)
+        except ImportError:
             pass
-        _cache[name] = klass
-        return klass
+        else:
+            klass = module.__postprocessor__
+    _cache[name] = klass
+    return klass
 
 
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