contrib: harfbuzz: revert version to 0.9.17

Starting with harfbuzz 0.9.18 there is a known crash.
Stay with 0.9.17 until this is fixed upstream.

refs #12425

contrib/src/harfbuzz/SHA512SUMS

-8df19497485acef4febc71bf908d4c983e6963766210bc400a79f6d59b8f405c53fe5a88c21683fa9c37a9e6befefe2efb0434f774d7f37924c522eae3b4ddd4  harfbuzz-0.9.19.tar.bz2
+0d10ba7075338b912f19a1a26d64502b772f5574a45fb43d92eaa56434cf5d2a844f23897ecb0abbdd26e1a0aec5f6ded7e533451ee6e4a03725f42aed7f9bcd  harfbuzz-0.9.17.tar.bz2

contrib/src/harfbuzz/rules.mak

 # HARFBUZZ
 
-HARFBUZZ_VERSION := 0.9.19
+HARFBUZZ_VERSION := 0.9.17
 HARFBUZZ_URL := http://www.freedesktop.org/software/harfbuzz/release/harfbuzz-$(HARFBUZZ_VERSION).tar.bz2
 PKGS += harfbuzz
 ifeq ($(call need_pkg,"harfbuzz"),)