This fixes a bug where
frame var a+5
returns the value a without any warning because the current logic simply ignores everything after ']' as long as there is no '.', '-' or '[' in the rest of the string.
The fix simplifies the termination condition of the expression path parsing loop to check if have a non-empty remaining string to parse. Previously, the condition checked if a separator was found. That condition coincided with the remaining string-to-parse condition except for the buggy indexed case where non-empty string was left ("+5" in the example above), but the separator index was 'npos'.