image.in/Makefile: fix show out image size again

The number of spaces may vary, so the column may be the sixth rather
than the fifth. As a result, we get an empty value and an error.
See commit c86141fc45

image.in/Makefile

@@ -90,7 +90,7 @@ imagedir:
 	@mkdir -p "$(IMAGE_OUTDIR)"
 
 postprocess: | $(addprefix postprocess-,$(sort $(POSTPROCESS_TARGETS)))
-	@OUTSIZE="`ls -lh "$(IMAGE_OUTPATH)" | cut -f5 -d' '`"; \
+	@OUTSIZE="`ls -lh "$(IMAGE_OUTPATH)" | tr -s " " | cut -f5 -d' '`"; \
 	if [ ! -n "$$OUTSIZE" ]; then \
 		echo "** error: $(IMAGE_OUTPATH) missing" >&2; \
 		exit 1; \