Fix more compile error/warnings for gcc-13

Fix more compile error/warnings for gcc-13

Remove these kind of warning messages

/home/leaf/work/dali-adaptor/dali/internal/addons/common/addon-manager.cpp:63:19: warning: moving a temporary object prevents copy elision [-Wpessimizing-move]
   63 |   return std::move(mImpl->LoadAddOns(addonNames));
/home/leaf/work/dali-adaptor/dali/internal/web-engine/common/web-engine-impl.cpp:59:19: warning: moving a temporary object prevents copy elision [-Wpessimizing-move]
   59 |   return std::move(fullName.str());
/home/leaf/work/dali-adaptor/dali/internal/imaging/common/webp-loading.cpp:220:19: warning: the address of ‘Dali::Internal::Adaptor::WebPLoading::Impl::mWebPData’ will never be NULL [-Waddress]
  220 |     if(&mWebPData != nullptr)

Change-Id: Icaa16235545d063ca6a555aa327930a7a5b8236e
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>