Improve exception message when spectrogram is empty

[swharden]

Abhinav e-mailed me indicating this library was throwing a divide-by-zero exception. It turned-out the problem was that it had some audio, but not enough to fill a full FFT column, and getting the bitmap would throw an exception.

[itsAbhi650]

Well, if you have Integrated width check I there won't be any need to do it manually everytime. Thanks

[swharden]

if you have Integrated width check I there won't be any need to do it manually every time

Yes and no. GetBitmap() returns a Bitmap, so the best I could do is have it check if Width is 0 and return null, but then your program would crash with a null reference exception (and an unhelpful message) if you try to call that object's Save() method.

I think the best behavior here is for GetBitmap() to throw an exception if there is insufficient data, and with e3b6e3f1603c4a2c331cee67fb438202edb47051 I updated the message to more clearly state what the issue was and how to fix it. It is published on NuGet now.

Thank you again for opening this issue!

[itsAbhi650]

Returning null when insufficient data.. that definitely make sense! and hey your welcome! That is what open source is all about 😄