Correctly handle the case when the LZMA include are in /usr/include

git-svn-id: http://root.cern.ch/svn/root/trunk@39728 27541ba8-7e3a-0410-8455-c3a389f83636

core/zip/Module.mk

@@ -96,4 +96,6 @@ distclean-$(MODNAME): clean-$(MODNAME)
 
 distclean::     distclean-$(MODNAME)
 
+ifneq ($(strip $(LZMAINCDIR)),)
 $(call stripsrc,$(MODDIRS))/R__LZMA.o: CFLAGS += -I$(LZMAINCDIR)
+endif