Merge pull request ExpressLRS#3473 from pkendall64/fix-gemini-K-modes

Clear the FEC encode buffer before use

Author: pkendall64

src/lib/LR1121Driver/LR1121.cpp

@@ -34,6 +34,7 @@ class CopyCodec final : public BufferCodec
 
 void ICACHE_RAM_ATTR FECCodec::encode(uint8_t *out, uint8_t *in, uint32_t len)
 {
+    memset(out, 0, len); // ensure that the buffer is zeroed to start
     FECEncode(in, out);
 }
 
@@ -643,7 +644,7 @@ void ICACHE_RAM_ATTR LR1121Driver::TXnb(uint8_t *data, const bool sendGeminiBuff
     }
 
     WORD_ALIGNED_ATTR uint8_t outBuffer[32] = {0};
-    const uint8_t length = PayloadLength+3;
+    const uint8_t length = PayloadLength + 3; // 3 extra zero bytes for the 24-bit timeout
     codec->encode(outBuffer, data, PayloadLength);
     if (sendGeminiBuffer)
     {