endless loop in jmespath::search

[MonkeybreadSoftware]

if the expression for jmespath::search contains an extra CR on the end, we get an endless loop.

It looks like advance_past_space_character detects we are >= end and thus sets ec to an error.
But ec is not checked.

So after calling advance_past_space_character(ec);, we may need to add if (ec) {return jmespath_expression();} to exit the loop.

[danielaparker]

Interesting edge case, I changed advance_past_space_character to allow it, since we already allow a CR followed by a space character (on master.)