level_cmd_load_model_from_geo and process_geo_layout should have debug assertions

[thecozies]

level_cmd_load_model_from_geo checks if the model you're loading is less than the model id count, but should throw an assertion if DEBUG Addressed: #722

also, when iterating the geolayout in in process_geo_layout , the first command should be verified to not be a bogus entry, iirc the only valid nodes would be GEO_CULLING_RADIUS (if an object geolayout this is fine) or GEO_NODE_START, there may be others im not thinking of, but this assertion would be for attempting to load a geolayout that doesnt exist. (it could just be in a different object group or whatever). the errors that this causes are really hard to track down because its likely that you would call way outside of the limit of GeoLayoutJumpTable