gloverlay: Fix various issues in allocation handling
- A copy-paste error was getting the information from the wrong query
- The 'allocation_meta' GstStructure was being leaked
- No check was done on whether the query existed (to try to set the resulting allocation meta on)
CID: 1439872 CID: 1439873 CID: 1439874 CID: 1439875 CID: 1439876 CID: 1439877