Fix #14126 crash in Tokenizer::simplifyCPPAttribute() (#7862)

Author: chrchr-github

lib/tokenize.cpp

@@ -9543,6 +9543,8 @@ void Tokenizer::simplifyCPPAttribute()
                 Token* head = skipCPPOrAlignAttribute(tok)->next();
                 while (isCPPAttribute(head) || isAlignAttribute(head))
                     head = skipCPPOrAlignAttribute(head)->next();
+                if (!head)
+                    syntaxError(tok);
                 head->isAttributeMaybeUnused(true);
             } else if (Token::findsimplematch(tok->tokAt(2), "unused", tok->link())) {
                 Token* head = skipCPPOrAlignAttribute(tok)->next();

test/testgarbage.cpp

@@ -257,6 +257,7 @@ class TestGarbage : public TestFixture {
         TEST_CASE(garbageCode226);
         TEST_CASE(garbageCode227);
         TEST_CASE(garbageCode228);
+        TEST_CASE(garbageCode229);
 
         TEST_CASE(garbageCodeFuzzerClientMode1); // test cases created with the fuzzer client, mode 1
 
@@ -1768,6 +1769,10 @@ class TestGarbage : public TestFixture {
         ASSERT_NO_THROW(checkCode("void f() { enum { A = [=]() mutable { return 0; }() }; }"));
         ASSERT_NO_THROW(checkCode("enum { A = [=](void) mutable -> int { return 0; }() };"));
     }
+    void garbageCode229() { // #14126
+        ASSERT_THROW_INTERNAL(checkCode("void f() {} [[maybe_unused]]"), SYNTAX);
+    }
+
 
     void syntaxErrorFirstToken() {
         ASSERT_THROW_INTERNAL(checkCode("&operator(){[]};"), SYNTAX); // #7818