fix(api): handle missing attribute in is_multi_lingual

[eginhard]

Fixes #3449, i.e. the following works again:

from TTS.api import TTS

cloud = TTS(model_name="tts_models/de/thorsten/vits")  # just to download the model
_ = cloud.tts("test")  # this works fine

from TTS.utils.generic_utils import get_user_data_dir
model = os.path.join(get_user_data_dir("tts"), "tts_models--de--thorsten--vits", "model_file.pth")
config = os.path.join(get_user_data_dir("tts"), "tts_models--de--thorsten--vits", "config.json")
local = TTS(model_path=model, config_path=config)
_ = local.tts("test")  # this failed previously

[stale]

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[nicemanis]

Why is this not merged?