Protect against reentrant dt_styles_apply_to_dev()

We must not apply all the requested history changes until the last request to do so
has finalized.
This can happen as reported in darktable-org#18311 (and elsewhere by lua calls to this function).

src/common/styles.c

@@ -1023,6 +1023,8 @@ void dt_styles_apply_to_dev(const char *name, const dt_imgid_t imgid)
     return;
   }
 
+  dt_pthread_mutex_lock(&darktable.dev_threadsafe);
+
   dt_print(DT_DEBUG_DEV | DT_DEBUG_PIPE,
     "[dt_styles_apply_to_dev] apply '%s' to darkroom ID=%d", name, imgid);
 
@@ -1044,6 +1046,7 @@ void dt_styles_apply_to_dev(const char *name, const dt_imgid_t imgid)
   dt_iop_connect_accels_all();
 
   dt_control_log(_("applied style `%s' on current image"), name);
+  dt_pthread_mutex_unlock(&darktable.dev_threadsafe);
 }
 
 void dt_styles_delete_by_name_adv(const char *name, const gboolean raise, const gboolean shortcut)