Ticket #5024: Don't crash upon invalid code when checking auto variables.

lib/checkautovariables.cpp

@@ -101,6 +101,9 @@ static bool checkRvalueExpression(const Token * const vartok)
 
 static bool variableIsUsedInScope(const Token* start, unsigned int varId, const Scope *scope)
 {
+    if(!start) // Ticket #5024
+        return false;
+    
     for (const Token *tok = start; tok != scope->classEnd; tok = tok->next()) {
         if (tok->varId() == varId)
             return true;

test/testautovariables.cpp

@@ -78,6 +78,7 @@ private:
         TEST_CASE(testautovar9);
         TEST_CASE(testautovar10); // ticket #2930 - void f(char *p) { p = '\0'; }
         TEST_CASE(testautovar11); // ticket #4641 - fp, assign local struct member address to function parameter
+        TEST_CASE(testautovar12); // ticket #5024 - crash
         TEST_CASE(testautovar_array1);
         TEST_CASE(testautovar_array2);
         TEST_CASE(testautovar_return1);
@@ -325,6 +326,10 @@ private:
               "}");
         ASSERT_EQUALS("[test.cpp:6]: (error) Address of local auto-variable assigned to a function parameter.\n", errout.str());
     }
+    
+    void testautovar12() { // Ticket #5024 - Crash on invalid input
+        check("void f(int* a) { a = }");
+    }
 
     void testautovar_array1() {
         check("void func1(int* arr[2])\n"