WM: ensure AlembicImportParams are always initialized

Initialize all members before assignment, ensuring newly added
members are never left uninitialized.

source/blender/editors/io/io_alembic.c

@@ -651,7 +651,7 @@ static int wm_alembic_import_exec(bContext *C, wmOperator *op)
     ED_object_mode_set(C, OB_MODE_OBJECT);
   }
 
-  struct AlembicImportParams params;
+  struct AlembicImportParams params = {};
   params.global_scale = scale;
   params.sequence_len = sequence_len;
   params.sequence_offset = offset;