RFR: JDK-8244018: No error message for non-existent icon path

[Andy Herrick]

Please review fix at [1] for issue [2]

The change just adds error when specified icon is not found, and a test 
for that.

/Andy

[1] - http://cr.openjdk.java.net/~herrick/8244018/webrev.01/

[2] - https://bugs.openjdk.java.net/browse/JDK-8244018