fix missing digit error translation

pkg/front_end/lib/src/scanner/errors.dart

Index: pkg/front_end/lib/src/scanner/errors.dart
diff --git a/pkg/front_end/lib/src/scanner/errors.dart b/pkg/front_end/lib/src/scanner/errors.dart
index 0139561eab9fdd6452b352b7233c31e1546a0ced..3a8483fae17d0b8cf20fbb65632f04f4d9de67cd 100644
--- a/pkg/front_end/lib/src/scanner/errors.dart
+++ b/pkg/front_end/lib/src/scanner/errors.dart
@@ -105,12 +105,12 @@ void translateErrorToken(ErrorToken token, ReportError reportError) {
     case ErrorKind.MissingExponent:
       // TODO(paulberry,ahe): Fasta reports the error location as the entire
       // number; analyzer expects the end of the number.
-      charOffset = endOffset;
+      charOffset = endOffset - 1;
       return _makeError(ScannerErrorCode.MISSING_DIGIT, null);
     case ErrorKind.ExpectedHexDigit:
       // TODO(paulberry,ahe): Fasta reports the error location as the entire
       // number; analyzer expects the end of the number.
-      charOffset = endOffset;
+      charOffset = endOffset - 1;
       return _makeError(ScannerErrorCode.MISSING_HEX_DIGIT, null);
     case ErrorKind.NonAsciiIdentifier:
     case ErrorKind.NonAsciiWhitespace: