Fix bug when the scanner does a pushback at the end of input.

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index bdf899b54df4fb53b699a2f5780e672b03f86bda..d7621825a975e5f2b5a91a266007b45ddbaff9f0 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -43,7 +43,7 @@ class BufferedUC16CharacterStream: public UC16CharacterStream {
   BufferedUC16CharacterStream();
   virtual ~BufferedUC16CharacterStream();
 
-  virtual void PushBack(uc16 character);
+  virtual void PushBack(uc32 character);
 
  protected:
   static const unsigned kBufferSize = 512;
@@ -107,11 +107,12 @@ class ExternalTwoByteStringUC16CharacterStream: public UC16CharacterStream {
                                            int end_position);
   virtual ~ExternalTwoByteStringUC16CharacterStream();
 
-  virtual void PushBack(uc16 character) {
+  virtual void PushBack(uc32 character) {
     ASSERT(buffer_cursor_ > raw_data_);
     buffer_cursor_--;
     pos_--;
   }
+
  protected:
   virtual unsigned SlowSeekForward(unsigned delta) {
     // Fast case always handles seeking.