package/znc: python support depends on icu

Upstream checks for icu when build with python support:
https://github.com/znc/znc/commit/4fe4a45dd62411ba9ede04750ca44f071e7d6cbb

Fixes
http://autobuild.buildroot.net/results/9e4/9e44159820789f1d25efcbd24318b0e05e132371/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/znc/znc.mk

@@ -32,7 +32,8 @@ else
 ZNC_CONF_OPTS += --disable-zlib
 endif
 
-ifeq ($(BR2_PACKAGE_PYTHON3),y)
+# python support depends on icu
+ifeq ($(BR2_PACKAGE_ICU)$(BR2_PACKAGE_PYTHON3),yy)
 ZNC_DEPENDENCIES += python3 host-swig
 ZNC_CONF_OPTS += --enable-python=python3
 else