Fix panic with an invalid filter expression that did not specify "valid parentheses syntax"

[AsaiYusuke]

Prior to this fix, there was a panic when a JSON path with an invalid filter expression that did not specify "valid parentheses syntax" was specified. A normal error should be returned for these syntax errors.

example: $.somewhere[?$.somewhere]

** I made the child pull request based on peter-jozsa's modifications to pull requests 21-23, so please let me complete the review of that one first.