[makefile] Inhibit warnings if AUTO_DEPS or MEDIA_DEPS are empty lists

src/Makefile.housekeeping

 #
 AUTO_DEPS	= $(patsubst %,$(BIN)/deps/%.d,$(AUTO_SRCS))
 ifdef NEED_DEPS
+ifneq ($(AUTO_DEPS),)
 -include $(AUTO_DEPS)
 endif
+endif
 autodeps :
 	@$(ECHO) $(AUTO_DEPS)
 VERYCLEANUP	+= $(BIN)/deps
 mediadeps :
 	@$(ECHO) $(MEDIA_DEPS)
 ifdef NEED_DEPS
+ifneq ($(MEDIA_DEPS),)
 -include $(MEDIA_DEPS)
 endif
+endif
 
 # Wrap up binary blobs (for embedded images)
 #