Fixed #5645: realloc return handling
static unsigned readChunk_tRNS(LodePNGColorMode* color, const unsigned char* data, size_t chunkLength)
{
  unsigned i;
  if(color->colortype == LCT_PALETTE)
  {
    /*error: more alpha values given than there are palette entries*/
    if(chunkLength > color->palettesize) return 38;

    for(i = 0; i < chunkLength; i++) color->palette[4 * i + 3] = data[i];
  }
  else if(color->colortype == LCT_GREY)
  {
    /*error: this chunk must be 2 bytes for greyscale image*/
    if(chunkLength != 2) return 30;

    color->key_defined = 1;
    color->key_r = color->key_g = color->key_b = 256u * data[0] + data[1];
  }
  else if(color->colortype == LCT_RGB)
  {
    /*error: this chunk must be 6 bytes for RGB image*/
    if(chunkLength != 6) return 41;

    color->key_defined = 1;
    color->key_r = 256u * data[0] + data[1];
    color->key_g = 256u * data[2] + data[3];
    color->key_b = 256u * data[4] + data[5];
  }
  else return 42; /*error: tRNS chunk not allowed for other color models*/

  return 0; /* OK */
}

static unsigned readChunk_tRNS(LodePNGColorMode* color, const unsigned char* data, size_t chunkLength)
{
  unsigned i;
  if(color->colortype == LCT_PALETTE)
  {
    /*error: more alpha values given than there are palette entries*/
    if(chunkLength > color->palettesize) return 38;

    for(i = 0; i < chunkLength; i++) color->palette[4 * i + 3] = data[i];
  }
  else if(color->colortype == LCT_GREY)
  {
    /*error: this chunk must be 2 bytes for greyscale image*/
    if(chunkLength != 2) return 30;

    color->key_defined = 1;
    color->key_r = color->key_g = color->key_b = 256u * data[0] + data[1];
  }
  else if(color->colortype == LCT_RGB)
  {
    /*error: this chunk must be 6 bytes for RGB image*/
    if(chunkLength != 6) return 41;

    color->key_defined = 1;
    color->key_r = 256u * data[0] + data[1];
    color->key_g = 256u * data[2] + data[3];
    color->key_b = 256u * data[4] + data[5];
  }
  else return 42; /*error: tRNS chunk not allowed for other color models*/

  return 0; /* OK */
}
