[gnome-calculator] lib: prevents segfault when elements of division to zero have null assigned tokens (fixes #769364)

[Alberto Ruiz <aruiz src gnome org>]

commit 647eb687821fd74764a55767bf1e34f68f5df940
Author: Alberto Ruiz <aruiz gnome org>
Date:   Mon Aug 1 09:30:48 2016 +0100

    lib: prevents segfault when elements of division to zero have null assigned tokens (fixes #769364)

 lib/equation-parser.vala |    6 +++++-
 tests/test-equation.vala |    1 +
 2 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/lib/equation-parser.vala b/lib/equation-parser.vala
index b00224d..994e11d 100644
--- a/lib/equation-parser.vala
+++ b/lib/equation-parser.vala
@@ -577,11 +577,15 @@ public class DivideNode : LRNode
         var z = l.divide (r);
         if (Number.error != null)
         {
+            uint token_start = 0;
+            uint token_end = 0;
             var tmpleft = right;
             var tmpright = right;
             while (tmpleft.left != null) tmpleft = tmpleft.left;
             while (tmpright.right != null) tmpright = tmpright.right;
-            parser.set_error (ErrorCode.MP, Number.error, tmpleft.token.start_index, 
tmpright.token.end_index);
+            if (tmpleft.token != null) token_start = tmpleft.token.start_index;
+            if (tmpright.token != null) token_end = tmpright.token.end_index;
+            parser.set_error (ErrorCode.MP, Number.error, token_start, token_end);
             Number.error = null;
         }
         return z;
diff --git a/tests/test-equation.vala b/tests/test-equation.vala
index 4a4d561..76d1250 100644
--- a/tests/test-equation.vala
+++ b/tests/test-equation.vala
@@ -346,6 +346,7 @@ private void test_equations ()
     test ("2÷3", "0.666666667", 0);
     test ("1÷0", "", ErrorCode.MP);
     test ("0÷0", "", ErrorCode.MP);
+    test ("1÷sin(0)", "", ErrorCode.MP);
 
     /* Precision */
     test ("1000000000000000−1000000000000000", "0", 0);