cleanup SDL_GetAudioDeviceSpec

- drop unnecessary hascapture check
- call SDL_InvalidParamError and return -1 in case the index is out of range
- do not zfill SDL_AudioSpec
- adjust documentation to reflect the behavior

include/SDL_audio.h

@@ -500,9 +500,7 @@ extern DECLSPEC const char *SDLCALL SDL_GetAudioDeviceName(int index,
  * hardware.
  *
  * `spec` will be filled with the sample rate, sample format, and channel
- * count. All other values in the structure are filled with 0. When the
- * supported struct members are 0, SDL was unable to get the property from the
- * backend.
+ * count.
  *
  * \param index the index of the audio device; valid values range from 0 to
  *              SDL_GetNumAudioDevices() - 1