asf: fix GUID reading on big endian platforms

Setting the initial parts (data1_, data2_, data3_) from the bytes
directly using memcpy() means that they will be interpreted depending
on the platform endianness. For example, the initial 4 bytes of the ASF
header are 0x30, 0x26, 0xB2, 0x75, which will be read as 0x3026B275 on
big endian platforms, never matching the actual GUID (0x75B22630), which
is always specified in little endian format.

Hence, when reading a GUID from data, make sure to turn the GUID parts
to little endian. This fixes the reading of ASF files on big endian
platforms.

Fixes commit bed8d3d

src/asfvideo.cpp

@@ -55,6 +55,11 @@ AsfVideo::GUIDTag::GUIDTag(const uint8_t* bytes) {
   memcpy(&data2_, bytes + DWORD, WORD);
   memcpy(&data3_, bytes + DWORD + WORD, WORD);
   std::copy(bytes + QWORD, bytes + 2 * QWORD, data4_.begin());
+  if (isBigEndianPlatform()) {
+    data1_ = byteSwap(data1_, true);
+    data2_ = byteSwap(data2_, true);
+    data3_ = byteSwap(data3_, true);
+  }
 }
 
 std::string AsfVideo::GUIDTag::to_string() {