loplugin:stringadd fix condition

Change-Id: I7752c281b1b6dd0d26bd7d6c4a6896c663f4cbc3
Reviewed-on: https://gerrit.libreoffice.org/80921
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/stringadd.cxx

@@ -264,7 +264,8 @@ bool StringAdd::isSideEffectFree(Expr const* expr)
             {
                 auto name = calleeMethodDecl->getName();
                 if (callExpr->getNumArgs() > 0
-                    && (name == "number" || name == "unacquired" || "boolean"))
+                    && (name == "number" || name == "unacquired" || name == "boolean"
+                        || name == "copy"))
                 {
                     auto tc = loplugin::TypeCheck(calleeMethodDecl->getParent());
                     if (tc.Class("OUString") || tc.Class("OString"))