[BUG] Merge Objects wouldn't merge two NodeGroups

**Describe the bug**

Merge Objects won't merge two NodeGroups properly on be1b1d4.

**To Reproduce**
1. Create the following graph named `MakeBox`:
2. Create the following graph named `DuplicateByDistance`:

**Expected behavior**
Merging Objects from these two NodeGroups should produce an object

3. Observe node groups working in isolation in the main graph:
produces
and
produces

4. However, joining them two
still produces only

additionally, the first node group outputs `Box: -` making it look like the box wasn't evaluated.

**Screenshots**
Screenshots provided above

**Desktop (please complete the following information):**
- OS: OSX
- Blender Version: 2.82
- Sorcar Version: be1b1d4

The issue is about the Merge Objects node failing to merge two NodeGroups in Sorcar, a Blender addon for procedural modeling. Look at the node graph logic in the Sorcar codebase, particularly the merge operation implementation. The screenshots show the expected vs actual behavior; start by reproducing the bug with the provided graphs. Check the NodeGroup evaluation and the Merge Objects node's handling of multiple inputs. The last comment is from 2294 days ago, so the codebase may have changed significantly.

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