Fix #14421 Crash in TokenList::isFunctionHead() (danmar#8146)

Co-authored-by: chrchr-github <noreply@github.com>

Author: chrchr-github

lib/tokenize.cpp

@@ -3343,9 +3343,12 @@ bool Tokenizer::simplifyUsing()
                     // function pointer
                     TokenList::copyTokens(tok1->next(), fpArgList, usingEnd->previous());
                     Token* const copyEnd = TokenList::copyTokens(tok1, start, fpQual->link()->previous());
-                    tok1->deleteThis();
+                    Token* leftPar = copyEnd->previous();
+                    while (leftPar->str() != "(")
+                        leftPar = leftPar->previous();
                     Token* const rightPar = copyEnd->next()->insertToken(")");
-                    Token::createMutualLinks(tok1->next(), rightPar);
+                    Token::createMutualLinks(leftPar, rightPar);
+                    tok1->deleteThis();
                     substitute = true;
                 } else if (fpArgList && !fpQual && Token::Match(tok1->next(), "* const| %name%")) {
                     // function pointer

test/testsimplifyusing.cpp

@@ -898,6 +898,14 @@ class TestSimplifyUsing : public TestFixture {
         const char expected2[] = "int ( * fp1 ) ( int ) ; int ( * const fp2 ) ( int ) ;";
         ASSERT_EQUALS(expected2, tok(code2));
         ASSERT_EQUALS("", errout_str());
+
+        const char code3[] = "using FP = std::string (*)();\n"
+                             "using FPC = std::string (*const)();\n"
+                             "FP fp;\n"
+                             "FPC fpc{};\n";
+        const char expected3[] = "std :: string ( * fp ) ( ) ; std :: string ( * const fpc ) ( ) { } ;";
+        ASSERT_EQUALS(expected3, tok(code3));
+        ASSERT_EQUALS("", errout_str());
     }
 
     void simplifyUsing8970() {