LanguageClient: avoid optional::value

Potentially throws std::bad_optional_access. Use operator* and
operator-> instead.

Change-Id: Idefa137da53f3663ea88961f1105b93402ec4777
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -169,7 +169,7 @@ public:
 
     bool detailIs(const QString &s) const
     {
-        return detail() && detail().value() == s;
+        return detail() && *detail() == s;
     }
 
     bool isMemberFunctionCall() const