revision: fix endless looping in revision parser

Fixes a bug in the revision parser which caused an endless loop when
parsing revisions with opening braces "{" but no closing braces "}".

Example bad revisions:

- ^{/
- ~@{
- @@{{0

1 files changed, 4 insertions, 0 deletions

diff --git a/internal/revision/parser.go b/internal/revision/parser.go
index 8facf17..8a2a719 100644
--- a/internal/revision/parser.go
+++ b/internal/revision/parser.go
@@ -322,6 +322,8 @@ func (p *Parser) parseAt() (Revisioner, error) {
 				}
 
 				return AtDate{t}, nil
+			case tok == eof:
+				return nil, &ErrInvalidRevision{s: `missing "}" in @{<data>} structure`}
 			default:
 				date += lit
 			}
@@ -424,6 +426,8 @@ func (p *Parser) parseCaretBraces() (Revisioner, error) {
 			p.unscan()
 		case tok != slash && start:
 			return nil, &ErrInvalidRevision{fmt.Sprintf(`"%s" is not a valid revision suffix brace component`, lit)}
+		case tok == eof:
+			return nil, &ErrInvalidRevision{s: `missing "}" in ^{<data>} structure`}
 		case tok != cbrace:
 			p.unscan()
 			re += lit