Fix OOB flash write when DFU interrupted

If a DFU is restarted, the write indices aren't reset causing the image to be written out of bounds. The CRC check prevents the faulty image from booting but LittleFS still gets nuked.

src/components/ble/DfuService.cpp

@@ -357,6 +357,8 @@ void DfuService::DfuImage::Init(size_t chunkSize, size_t totalSize, uint16_t exp
   this->totalSize = totalSize;
   this->expectedCrc = expectedCrc;
   this->ready = true;
+  totalWriteIndex = 0;
+  bufferWriteIndex = 0;
 }
 
 void DfuService::DfuImage::Append(uint8_t* data, size_t size) {