Fix startup race condition

Fixrare  race condition between OpenCL background job
and `dt_wb_presets_init`.

In darktable.c:1878-1887, the GUI startup path queues OpenCL detection as a background job on the system worker pool and then immediately continues to call `dt_wb_presets_init(NULL)`.

`dt_opencl_init` (called by a worker thread) loads OpenCL vendor libraries (ICD loader, driver). These vendor libraries are known to call `setlocale()` internally.
`setlocale()` in glibc:
* Acquires `__libc_setlocale_lock`
* Frees and replaces internal locale data structures (including cached locale strings)

Meanwhile, the main thread is inside `dcigettext` → `guess_category_value` → `getenv("LANGUAGE")`. The glibc `dcigettext` code is not re-entrant with `setlocale()`: it caches locale state that can be freed mid-read when `setlocale()` runs concurrently, leading to a SIGSEGV.
This does not happen in the non-GUI/CLI path (`init_gui=0`) because there `dt_opencl_init` is called synchronously before `dt_wb_presets_init`.

Potential fixes:
* Move `dt_wb_presets_init` (and `dt_noiseprofile_init`) to before the OpenCL background job is enqueued, so the JSON/gettext code finishes before any worker thread starts running the OCL job. In darktable.c around line 1876. The fix is confirmed clean for the non-GUI path since it already calls `dt_opencl_init` synchronously — the proposed reorder makes both paths consistent.
* Alternatively, a more targeted fix is to call `setlocale(LC_ALL, "")` once and freeze it (or save/restore it around `dt_opencl_init`) before JSON parsing begins, but reordering the init sequence is cleaner and less invasive.

Author: da-phil

src/common/darktable.c

@@ -1873,23 +1873,25 @@ int dt_init(int argc,
   heif_init(NULL);
 #endif
 
+  dt_splash_screen_set_progress(_("initializing WB presets"));
+  dt_wb_presets_init(NULL);
+
+  // Do locale-sensitive init BEFORE starting any background worker jobs
+  dt_splash_screen_set_progress(_("loading noise profiles"));
+  darktable.noiseprofile_parser = dt_noiseprofile_init(noiseprofiles_from_command);
+
   dt_splash_screen_set_progress(_("starting OpenCL"));
   darktable.opencl = (dt_opencl_t *)calloc(1, sizeof(dt_opencl_t));
+  darktable.points = (dt_points_t *)calloc(1, sizeof(dt_points_t));
+  dt_points_init(darktable.points, dt_get_num_threads());
+
+  // Only then kick off the OpenCL background job
   if(init_gui)
     dt_control_add_job(DT_JOB_QUEUE_SYSTEM_BG, _detect_opencl_job_create(exclude_opencl));
   else
     dt_opencl_init(darktable.opencl, exclude_opencl, print_statistics);
 
-  darktable.points = (dt_points_t *)calloc(1, sizeof(dt_points_t));
-  dt_points_init(darktable.points, dt_get_num_threads());
-
-  dt_wb_presets_init(NULL);
-
-  dt_splash_screen_set_progress(_("loading noise profiles"));
-  darktable.noiseprofile_parser = dt_noiseprofile_init(noiseprofiles_from_command);
-
-  // must come before mipmap_cache, because that one will need to access
-  // image dimensions stored in here:
+  // must come before mipmap_cache, because that one will need to access image dimensions stored in here:
   dt_image_cache_init();
 
   dt_mipmap_cache_init();