Fix T100737: OBJ/USD import: imported object has no active material, material has 2 users

Fixes issues in importers written in C++ (T100737):

- Materials had one reference count too much. Affected Collada,
  Alembic, USD, OBJ importers, looks like "since forever".
- Active material index was not properly set on imported meshes.
  Regression since 3.3 (D15145). Affected Alembic, USD, OBJ. Note:
  now it sets the first material as the active one, whereas
  previously the last one was set as active. First one sounds more
  "intuitive" to me.

Reviewed By: Bastien Montagne
Differential Revision: https://developer.blender.org/D15831

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/io/collada/DocumentImporter.cpp b/source/blender/io/collada/DocumentImporter.cpp
index 2ce97bc8b5d..1ffe412b3ed 100644
--- a/source/blender/io/collada/DocumentImporter.cpp
+++ b/source/blender/io/collada/DocumentImporter.cpp
@@ -743,6 +743,7 @@ bool DocumentImporter::writeMaterial(const COLLADAFW::Material *cmat)
   const std::string &str_mat_id = cmat->getName().empty() ? cmat->getOriginalId() :
                                                             cmat->getName();
   Material *ma = BKE_material_add(bmain, (char *)str_mat_id.c_str());
+  id_us_min(&ma->id);
 
   this->uid_effect_map[cmat->getInstantiatedEffect()] = ma;
   this->uid_material_map[cmat->getUniqueId()] = ma;