Fix uninitialized values identified by cppcheck

* Replace `malloc` by `calloc` for c-string initialization
* Add initializer braces for structs

src/modules/ekf2_replay/ekf2_replay_main.cpp

@@ -839,7 +839,7 @@ void Ekf2Replay::task_main()
 
 	// create path which tells user location of replay file
 	char tmp2[] = "./build_posix_sitl_replay/src/firmware/posix";
-	char *replay_file_location = (char *) malloc(1 + strlen(tmp) + strlen(tmp2) + strlen(replay_log_name));
+	char *replay_file_location = (char *) calloc(1 + strlen(tmp) + strlen(tmp2) + strlen(replay_log_name), 1);
 	strcat(replay_file_location, tmp2);
 	strcat(replay_file_location, replay_log_name);
 	strcat(replay_file_location, tmp);

src/modules/uORB/uORB_tests/uORBTest_UnitTest.cpp

@@ -317,7 +317,7 @@ int uORBTest::UnitTest::test_multi()
 	/* this routine tests the multi-topic support */
 	test_note("try multi-topic support");
 
-	struct orb_test t, u;
+	struct orb_test t {}, u {};
 	t.val = 0;
 	int instance0;
 	_pfd[0] = orb_advertise_multi(ORB_ID(orb_multitest), &t, &instance0, ORB_PRIO_MAX);
@@ -536,7 +536,7 @@ int uORBTest::UnitTest::test_multi_reversed()
 		return test_fail("sub. id2: ret: %d", sfd2);
 	}
 
-	struct orb_test t, u;
+	struct orb_test t {}, u {};
 
 	t.val = 0;