clang-tidy: replace memcpy with copy_n

Found with bugprone-not-null-terminated-result

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/jpgimage.cpp

@@ -1001,7 +1001,7 @@ int ExvImage::writeHeader(BasicIo& outIo) const {
   byte tmpBuf[7];
   tmpBuf[0] = 0xff;
   tmpBuf[1] = 0x01;
-  std::memcpy(tmpBuf + 2, exiv2Id_, 5);
+  std::copy_n(exiv2Id_, 5, tmpBuf + 2);
   if (outIo.write(tmpBuf, 7) != 7)
     return 4;
   if (outIo.error())

src/value.cpp

@@ -471,7 +471,7 @@ size_t XmpValue::copy(byte* buf, ByteOrder /*byteOrder*/) const {
   write(os);
   std::string s = os.str();
   if (!s.empty())
-    std::memcpy(buf, s.data(), s.size());
+    std::copy_n(s.data(), s.size(), buf);
   return s.size();
 }