more fixes for fasta analyzer integration

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

Index: pkg/analyzer/lib/src/dart/scanner/scanner.dart
diff --git a/pkg/analyzer/lib/src/dart/scanner/scanner.dart b/pkg/analyzer/lib/src/dart/scanner/scanner.dart
index de666a63743214489b0ab1da41842466057e2d03..e2c0aa0113390437dabe8ab2dae032b1f5468a06 100644
--- a/pkg/analyzer/lib/src/dart/scanner/scanner.dart
+++ b/pkg/analyzer/lib/src/dart/scanner/scanner.dart
@@ -137,11 +137,11 @@ class _Scanner2 implements Scanner {
 
   @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);
     }