fix some implicit conversions

Found with warning C4267

Signed-off-by: Rosen Penev <[email protected]>

Author: neheb

src/MemIOCallback.cpp

@@ -91,7 +91,7 @@ std::size_t MemIOCallback::write(IOCallback & IOToRead, std::size_t Size)
   }
   IOToRead.readFully(&dataBuffer[dataBufferPos], Size);
   dataBufferTotalSize = Size;
-  return Size;
+  return static_cast<std::uint32_t>(Size);
 }
 
 } // namespace libebml

src/StdIOCallback.cpp

@@ -98,7 +98,7 @@ void StdIOCallback::setFilePointer(std::int64_t Offset,seek_mode Mode)
 std::size_t StdIOCallback::write(const void*Buffer,std::size_t Size)
 {
   assert(File!=nullptr);
-  const std::uint32_t Result = fwrite(Buffer,1,Size,File);
+  const size_t Result = fwrite(Buffer,1,Size,File);
   mCurrentPosition += Result;
   return Result;
 }