Patch release.

This patch reintroduces pugixml target for CMake when find_package is used, which was accidentally removed from v1.11.
It's recommended that pugixml::pugixml target is used instead, but this patch restores pugixml target for existing applications / libraries that depend on it.

The previous patch, v1.11.3, did not handle repeated attempts to call find_package; this patch fixes that particular corner case.