Download chartjs only once in makefile (#1524)

### WHAT is this pull request doing?
Currently we download chart.js twice, and check sha256sum twice. Since
we run make multi-threaded, it is possible that the file is
deleted before the step is completed, meaning the package can end up
without the correct files.

This changes that to only download chart.js once, to make sure the file
can not be deleted between build steps

This also adds an exit if the sha256sum fails. 

### HOW can this pull request be tested?
run `make js`, verify output

Author: viktorerlingsson

Makefile

@@ -63,17 +63,20 @@ lib: shard.yml shard.lock
 bin static/js/lib man1 static/js/lib/chunks:
 	mkdir -p $@
 
-static/js/lib/chart.js: | static/js/lib
+.PHONY: chart.js.tgz
+chart.js.tgz:
 	curl --fail --retry 5 -sL -o chart.js.tgz https://github.com/chartjs/Chart.js/releases/download/v4.0.1/chart.js-4.0.1.tgz && \
-		echo "461dae2edc0eda7beeb16c7030ab630ab5129aedd3fc6de9a036f6dfe488556f chart.js.tgz" | sha256sum -c - && \
-		tar -zxOf chart.js.tgz package/dist/chart.js > $@ ; \
-		(rm -f chart.js.tgz && echo "removed chart.js.tgz")
+	echo "461dae2edc0eda7beeb16c7030ab630ab5129aedd3fc6de9a036f6dfe488556f chart.js.tgz" | sha256sum -c - || (rm -f chart.js.tgz && exit 1)
 
-static/js/lib/chunks/helpers.segment.js: | static/js/lib/chunks
-	curl --fail --retry 5 -sL -o chart.js.tgz https://github.com/chartjs/Chart.js/releases/download/v4.0.1/chart.js-4.0.1.tgz && \
-		echo "461dae2edc0eda7beeb16c7030ab630ab5129aedd3fc6de9a036f6dfe488556f chart.js.tgz" | sha256sum -c - && \
-		tar -zxOf chart.js.tgz package/dist/chunks/helpers.segment.js > $@ ; \
-		(rm -f chart.js.tgz && echo "removed chart.js.tgz")
+.PHONY: after-chartjs
+after-chartjs: static/js/lib/chart.js static/js/lib/chunks/helpers.segment.js
+	rm -f chart.js.tgz
+
+static/js/lib/chart.js: | static/js/lib chart.js.tgz
+		tar -zxOf chart.js.tgz package/dist/chart.js > $@
+
+static/js/lib/chunks/helpers.segment.js: | static/js/lib/chunks chart.js.tgz
+		tar -zxOf chart.js.tgz package/dist/chunks/helpers.segment.js > $@
 
 static/js/lib/luxon.js: | static/js/lib
 	curl --fail --retry 5 -sLo $@ https://moment.github.io/luxon/es6/luxon.mjs && \
@@ -111,7 +114,7 @@ MANPAGES := man1/lavinmq.1 man1/lavinmqctl.1 man1/lavinmqperf.1
 man: $(MANPAGES)
 
 .PHONY: js
-js: $(JS)
+js: $(JS) after-chartjs
 
 .PHONY: deps
 deps: js lib