[gnome-calculator] Fix crash issues due to null pointer dereference

[Arth Patel <arthpatel src gnome org>]

commit 3c55d33e6953fb49b2dc5f3ea4dd72438e106539
Author: PioneerAxon <arth svnit gmail com>
Date:   Tue Mar 26 02:01:54 2013 +0530

    Fix crash issues due to null pointer dereference

 src/equation-lexer.vala |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/src/equation-lexer.vala b/src/equation-lexer.vala
index f012168..6d62f4d 100644
--- a/src/equation-lexer.vala
+++ b/src/equation-lexer.vala
@@ -276,12 +276,9 @@ public class Lexer
     /* Get next token interface. Will be called by parser to get pointer to next token in token stream. */
     public LexerToken get_next_token ()
     {
-        var token = tokens.nth_data (next_token);
-        next_token++;
         if (next_token >= tokens.length ())
-            next_token = tokens.length ();
-       
-        return token;
+            return tokens.nth_data (tokens.length () - 1);
+        return tokens.nth_data (next_token++);
     }
 
     /* Roll back one lexer token. */