hud_rainbow: disable draw rainbow color player names in spectator mode #123

Job	Run time
Android	1m 56s
build (ubuntu-latest, gcc, g++)	1m 43s
build (ubuntu-latest, clang, clang++)	1m 26s
build (windows-2019, cl, cl)	1m 49s
Release	1m 7s
	8m 1s

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