fix: respect caller-provided waveform for PTT audio messages

When sending PTT audio with an explicit waveform, Baileys unconditionally
overwrites it with getAudioWaveform() which returns undefined when
audio-decode is not installed — resulting in a flat line on WhatsApp.

Now only invokes getAudioWaveform() when no waveform is already provided,
matching the existing pattern used for jpegThumbnail (line 241).

Validated via CDP + Frida interception: WhatsApp waveform format is
64 bytes Uint8Array, values 0-99, byte-for-byte identical between
Android (audio_data table) and WA Web (model-storage IDB).

Ref: WhiskeySockets/Baileys#2443

Co-Authored-By: Renato Alcara

src/Utils/messages.ts

@@ -297,7 +297,7 @@ export const prepareWAMessageMedia = async (
 					logger?.debug('computed audio duration')
 				}
 
-				if (requiresWaveformProcessing) {
+				if (requiresWaveformProcessing && !uploadData.waveform) {
 					uploadData.waveform = await getAudioWaveform(filePath, logger)
 					logger?.debug('processed waveform')
 				}