Fix #136645: Regression: Preview generation fails for multiple IDs

Fixes: #136842, #136645

Caused by 76d6d169ba
When multiple objects are selected to mark as assets, preview generation
job of previous ID in the for loop is cleared by `ED_preview_kill_jobs`
inside `generate_preview`. To fix this, check if `id->preview` exists then
clear the preview job if exists inside the new function
`ED_preview_kill_jobs_for_id`.
Solution proposed by @JulianEisel. I came up with idea to use `wm_job_find`

Pull Request: https://projects.blender.org/blender/blender/pulls/136918

source/blender/editors/asset/intern/asset_mark_clear.cc

@@ -61,7 +61,7 @@ void generate_preview(const bContext *C, ID *id)
     return;
   }
 
-  ED_preview_kill_jobs(CTX_wm_manager(C), CTX_data_main(C));
+  ED_preview_kill_jobs_for_id(CTX_wm_manager(C), id);
 
   PreviewImage *preview = BKE_previewimg_id_get(id);
   if (preview) {

source/blender/editors/include/ED_render.hh

@@ -113,6 +113,7 @@ void ED_preview_restart_queue_add(ID *id, enum eIconSizes size);
 void ED_preview_restart_queue_work(const bContext *C);
 
 void ED_preview_kill_jobs(wmWindowManager *wm, Main *bmain);
+void ED_preview_kill_jobs_for_id(wmWindowManager *wm, const ID *id);
 
 void ED_preview_draw(
     const bContext *C, void *idp, void *parentp, void *slotp, uiPreview *ui_preview, rcti *rect);

source/blender/editors/render/render_preview.cc

@@ -2171,6 +2171,14 @@ void ED_preview_kill_jobs(wmWindowManager *wm, Main * /*bmain*/)
   }
 }
 
+void ED_preview_kill_jobs_for_id(wmWindowManager *wm, const ID *id)
+{
+  const PreviewImage *preview = BKE_previewimg_id_get(id);
+  if (wm && preview) {
+    WM_jobs_kill_type(wm, preview, WM_JOB_TYPE_RENDER_PREVIEW);
+  }
+}
+
 struct PreviewRestartQueueEntry {
   PreviewRestartQueueEntry *next, *prev;