Fix #13692 fuzzing crash (null-pointer-use) in Tokenizer::simplifyAsm() (danmar#8094)

Author: chrchr-github

lib/tokenize.cpp

@@ -9976,6 +9976,8 @@ void Tokenizer::simplifyAsm()
                 instruction = tok->stringifyList(endasm);
                 Token::eraseTokens(tok, endasm);
             } else if (!endasm) {
+                if (!tok->next())
+                    syntaxError(tok);
                 instruction = tok->next()->stringifyList(endasm);
                 Token::eraseTokens(tok, endasm);
                 tok->insertToken(";");

test/cli/fuzz-crash/crash-7d409757e9b94fc2eb23758b655e056ec3dd9d09

@@ -0,0 +1 @@
+_asm