Fix #14573 Only consider last NULL argument in varFuncNullUB (cppcheck-opensource#8297)

Resolving a FP in which the expanded macro ensures that the last
variadic argument is not NULL.

Author: mptre

lib/checkother.cpp

@@ -3557,7 +3557,7 @@ void CheckOther::checkVarFuncNullUB()
     for (const Scope * scope : symbolDatabase->functionScopes) {
         for (const Token* tok = scope->bodyStart; tok != scope->bodyEnd; tok = tok->next()) {
             // Is NULL passed to a function?
-            if (Token::Match(tok,"[(,] NULL [,)]")) {
+            if (Token::Match(tok,"[(,] NULL )")) {
                 // Locate function name in this function call.
                 const Token *ftok = tok;
                 int argnr = 1;

test/testother.cpp

@@ -11309,6 +11309,12 @@ class TestOther : public TestFixture {
         check("void a(char *p, ...);\n"
               "void b() { a(NULL, 2); }");
         ASSERT_EQUALS("", errout_str());
+
+        checkP("extern const int sentinel;\n"
+               "void a(int, ...);\n"
+               "#define b(x, ...) a((x), __VA_ARGS__, &sentinel)\n"
+               "void c() { b(1, NULL); }");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void checkCastIntToCharAndBack() { // #160