[png] Do not find zlib within the libPng CMakeLists.txt

Author: dpiparo

builtins/libpng/CMakeLists.txt

@@ -40,8 +40,9 @@ ExternalProject_Add(
     -DCMAKE_CXX_VISIBILITY_PRESET=hidden
     -DPNG_SHARED=OFF
     -DPNG_STATIC=ON
-    -DZLIB_INCLUDE_DIR=${ZLIB_INCLUDE_DIRS}
-    -DZLIB_LIBRARY=${ZLIB_LIBRARIES}
+    -DZLIB_INCLUDE_DIRS=${ZLIB_INCLUDE_DIRS}
+    -DZLIB_LIBRARIES=${ZLIB_LIBRARIES}
+    -DZLIB_FOUND=${ZLIB_FOUND}
     BUILD_COMMAND ${CMAKE_COMMAND} --build . ${ROOT_LIBPNG_BUILD_COMMAND_FLAGS}
     INSTALL_COMMAND ${CMAKE_COMMAND} --build . ${ROOT_LIBPNG_BUILD_COMMAND_FLAGS} --target install
     LOG_CONFIGURE 1 LOG_BUILD 1 LOG_INSTALL 1 LOG_OUTPUT_ON_FAILURE 1