Use default value on no match regardless of ElementConverter presence

[veyndan]

Closes #72.

When no match occurs, Jspoon should use the default value given by the user instead of passing null to the node of ElementConverter. ElementConverter shouldn't receive null as the Javadoc of Selector#converter states that the converter should only be used for matched (i.e. non-null) elements:

jspoon/jspoon/src/main/java/pl/droidsonroids/jspoon/annotation/Selector.java

Lines 66 to 68 in 2159364

	/** @return The converter to be used for the matched {@link Element element} */
	@SuppressWarnings("rawtypes")
	Class<? extends ElementConverter> converter() default ElementConverter.class;