cpp: Check fpr of import status for NULL

* lang/cpp/src/importresult.cpp (GpgME::ImportResult::Private): Check
fpr for NULL.
--

GnuPG-bug-id: 5713

lang/cpp/src/importresult.cpp

@@ -48,7 +48,9 @@ public:
         // We just need to handle the pointers in the structs:
         for (gpgme_import_status_t is = r.imports ; is ; is = is->next) {
             gpgme_import_status_t copy = new _gpgme_import_status(*is);
+            if (is->fpr) {
                 copy->fpr = strdup(is->fpr);
+            }
             copy->next = nullptr;
             imports.push_back(copy);
         }