Fixes a Terminal FIFO full issue that caused data to be lost. The Unicode and EFI Key FIFOs are now checked to make sure they have spaces before pushing another entry. Signed-off-by: eugenecohen Reviewed-by: niruiyu git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12512 6f19259b-4bc3-4df7-8a09-765794883524