Strict mode errors on unless block with nested property

[GriffinSauce]

When strict: true is added Handlebars errors on the use of a missing nested property in an unless block helper.

var myObject = {};

{{#unless myObject}}

{{/unless}}
-> no error

{{#unless myObject.prop.prop}}

{{/unless}}
-> error "prop doesn't exist"

As described in this issue strict mode shouldn't be enforced on helpers and conditional block. The point of a conditional block is to handle (non-)existence of properties.

[kpdecker]

Right now arguments are basically treated the same was as assumeObjects mode for strict mode. It doesn't seem out of line to change this to perform normal object existence checks (which come at the expense of a larger codebase).

If strict mode is defined and assumeObjects is not, then we should do the existence check for arg and hash lookups. If assumeObjects is set, then it should throw as it does today.