Android: Fix for uncaught java exception.

If an exception's getMessage() function returns a null object, we can't
send it directly to the Log function, as it will throw an exception...
To avoid this we can prepend the string from getMessage() with an empty
string.

Change-Id: Ie026cbf9af133352919a4536c152b6d35cb8c0a7
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>