active_map_test: use vpx_active_map_t() to initialize vars

0-initializes [1] and removes a warning for missing initializer fields

[1] http://en.cppreference.com/w/cpp/language/value_initialization

Change-Id: I886fa72c74679b52cdce2af3364172395a5b6a51

test/active_map_test.cc

@@ -38,7 +38,7 @@ class ActiveMapTest
     if (video->frame() == 1) {
       encoder->Control(VP8E_SET_CPUUSED, cpu_used_);
     } else if (video->frame() == 3) {
-      vpx_active_map_t map = {0};
+      vpx_active_map_t map = vpx_active_map_t();
       uint8_t active_map[9 * 13] = {
         1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0,
         1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0,
@@ -57,7 +57,7 @@ class ActiveMapTest
       map.active_map = active_map;
       encoder->Control(VP8E_SET_ACTIVEMAP, &map);
     } else if (video->frame() == 15) {
-      vpx_active_map_t map = {0};
+      vpx_active_map_t map = vpx_active_map_t();
       map.cols = (kWidth + 15) / 16;
       map.rows = (kHeight + 15) / 16;
       map.active_map = NULL;