PHP notice when you add an issue without a version

While working on #376377: Issue + organic group incompatibility and #405478: Do a proper page/code split of project_issue on a totally clean test site (not using the d.o install profile), I found that you get PHP notices when you create new issues if project_release is enabled but there are no releases for a project yet. Trivial patch, just wanted an issue about it for the commit.