[Tizen][Runtime] Fix allow-navigation element can not take effect if there are more than 1 tags in config.xml

In Tizen core spec (https://source.tizen.org/sites/default/files/page/tizen-2.2-wrt-core-spec.pdf), it's said that "if more than 1, the first occurrence MUST be considered (and all others ignored)." This patch makes the runtime following the spec.

BUG=XWALK-1696