Library: don't prevent adding a new directory if an existing dir is m…

…issing

It is checked whether the new directory exists beforehand, therefor the checks below
can not be tricked and no inconsistences should arise

src/library/dao/directorydao.cpp

@@ -78,7 +78,7 @@ DirectoryDAO::AddResult DirectoryDAO::addDirectory(
                     << ": Loaded directory"
                     << oldDir.location()
                     << "does not exist or is inaccessible";
-            return AddResult::InvalidOrMissingDirectory;
+            continue;
         }
         const auto oldCanonicalLocation = oldDir.canonicalLocation();
         DEBUG_ASSERT(!oldCanonicalLocation.isEmpty());