Fix memset on std::vector error in ubrowser initialization

Fix memset on std::vector error in ubrowser initialization

In file ewk/ubrowser/main.cc in function main there was memset function
used on an AppData struct, which contains a std::vector member. Memset
on a std::vector can destroy its private data and lead to unexpected
behavior.

Fixed by removing memset and zeroing other members of AppData struct
in its constructor.

This error was reported by cppcheck static analysis tool.

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=15002

Reviewed by: a.renevier, a1.gomes, d.waslicki, sns.park

Change-Id: Ibaa89e4fa97e88f094f94beaac3318122c61b16b
Signed-off-by: Grzegorz Ludwikowski <g.ludwikowsk@samsung.com>