Raise ImportError and not ValueError when sqlite3 is missing

Excepting ValueError when creating the SQLiteSession could hide
other errors (e.g. using a newer session file on an older version
of the library). Instead, the original error is raised, as if
sqlite3 was being imported within its __init__ method.

telethon/client/telegrambaseclient.py

@@ -202,7 +202,7 @@ class TelegramBaseClient(abc.ABC):
         if isinstance(session, str) or session is None:
             try:
                 session = SQLiteSession(session)
-            except ValueError:
+            except ImportError:
                 import warnings
                 warnings.warn(
                     'The sqlite3 module is not available under this '