Fixed #2653 (segmentation fault of cppcheck 'x=b=0;')

lib/tokenize.cpp

@@ -6095,7 +6095,6 @@ void Tokenizer::simplifyVariableMultipleAssign()
         if (Token::Match(tok, "%var% = %var% = %num% ;") ||
             Token::Match(tok, "%var% = %var% = %var% ;"))
         {
-
             // skip intermediate assignments
             Token *tok2 = tok->previous();
             while (tok2 &&
@@ -6105,7 +6104,7 @@ void Tokenizer::simplifyVariableMultipleAssign()
                 tok2 = tok2->tokAt(-2);
             }
 
-            if (tok2->str() != ";")
+            if (!tok2 || tok2->str() != ";")
             {
                 continue;
             }

test/testtokenize.cpp

@@ -326,6 +326,9 @@ private:
 
         // Some simple cleanups of unhandled macros in the global scope
         TEST_CASE(removeMacrosInGlobalScope);
+
+        // a = b = 0;
+        TEST_CASE(multipleAssignment);
     }
 
 
@@ -5618,6 +5621,11 @@ private:
         // remove some unhandled macros in the global scope.
         ASSERT_EQUALS("void f ( ) { }", tokenizeAndStringify("void f() NOTHROW { }"));
     }
+
+    void multipleAssignment()
+    {
+        ASSERT_EQUALS("a = b = 0 ;", tokenizeAndStringify("a=b=0;"));
+    }
 };
 
 REGISTER_TEST(TestTokenizer)