FIX 'NoneType' object has no attribute 'isalpha' (#2440)

passerbya

2025-03-20 5ee2f382b32c5c0beaa1c133b466a100c6fb7ebc

 runtime/csharp/AliParaformerAsr/AliParaformerAsr/WavFrontend.cs

@@ -30,7 +30,8 @@
            _fbank_beg_idx = 0;
            _onlineFbank = new OnlineFbank(
                dither: _frontendConfEntity.dither,
                snip_edges: false,
                snip_edges: _frontendConfEntity.snip_edges,
                window_type: _frontendConfEntity.window,
                sample_rate: _frontendConfEntity.fs,
                num_bins: _frontendConfEntity.n_mels
                );