Handle tag/branches that don't have output yet

makefile

@@ -197,7 +197,7 @@ require_inputdir = $(or $(strip $(INPUTDIR)),fail)
 
 .PHONY: sync_pre
 sync_pre: | $(require_inputdir)
-	$(foreach TARGET,$(TARGETS),
+	$(foreach TARGET,$(TARGETS),mkdir -p $(INPUTDIR)/$(OUTPATH);
 		find $(INPUTDIR)/$(OUTPATH)/ -maxdepth 1 -type f \( \
 				-name "$(TARGET)*" \
 				$(and $(call printisbn,$(TARGET)),-or -name "$(call printisbn,$(TARGET))*") \