Fix crash in UnixPkg caused by r10769. The DxeCore is not calling the library constru...

Fix crash in UnixPkg caused by r10769. The DxeCore is not calling the library constructor, but is calling the library members that are coded to assume the constructor has run. Check to make sure constructor has run before using services. If Dxe Core starts calling library constructor then this code will just work, but it may cause an issue with the extra call to load symbols, since we catch the symbol load in DxeIpl.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10774 6f19259b-4bc3-4df7-8a09-765794883524