more fixes for fasta analyzer integration

pkg/analyzer/lib/src/dart/scanner/scanner.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.dart.scanner.scanner;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/error/syntactic_errors.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
@@ skipping 119 matching lines @@
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     _errorListener
         .onError(new AnalysisError(source, offset, 1, errorCode, arguments));
   }
 
   @override
   void setSourceStart(int line, int column) {
-    lineStarts.removeAt(0);
     int offset = _readerOffset;
     if (line < 1 || column < 1 || offset < 0 || (line + column - 2) >= offset) {
       return;
     }
+    lineStarts.removeAt(0);
     for (int i = 2; i < line; i++) {
       lineStarts.add(1);
     }
     lineStarts.add(offset - column + 1);
   }
 
   @override
   Token get tail {
     throw 'unsupported operation';
   }
@@ skipping 29 matching lines @@
       } while (!token.isEof);
     }
     return firstToken;
   }
 
   @override
   set preserveComments(bool preserveComments) {
     this._preserveComments = preserveComments;
   }
 }