Initial { of binding can be swallowed, causing a false positive binding

[Spencer Hamm]

Describe the bug

A binding like {foo.bar will have the { swallowed, causing it to be a false binding of two identifiers without the {

To Reproduce

player/core/player/src/binding-grammar/custom/index.ts

Line 140 in 24a7f7b

 next(OPEN_CURL); 

Expected behavior

Error is thrown when two { aren't adjacent to each other.