Update error location when unexpectedly parsing binder

[andrevidela]

Steps to Reproduce

mayBeesToMaybe : List (Maybe a) -> Maybe (List a)                                                                     
mayBeesToMaybe (x :: xs) = case x of                                                                                   
                                _ => Just (x : xs)   

Expected Behavior

Error: Unexpected binder in application.

ParserErrorHelp:4:35--4:37
 1 | 
 2 | mayBeesToMaybe : List (Maybe a) -> Maybe (List a)
 3 | mayBeesToMaybe (x :: xs) = case x of
 4 |                                 _ => Just (x : xs)
                                               ^^^^^^^^

Observed Behavior

Error: Expected '=>' or 'impossible'.

ParserErrorHelp:4:35--4:37
 1 | 
 2 | mayBeesToMaybe : List (Maybe a) -> Maybe (List a)
 3 | mayBeesToMaybe (x :: xs) = case x of
 4 |                                 _ => Just (x : xs)
                                       ^^