Sculpt curves: Fix BKE_paint_object_mode_from_paintmode

Currently harmless (since atm. it is not possible to trigger this part
of the code from curves sculpting), but in a future fix (for T101518), it
would be good to use `BKE_paint_init` (and having the correct ob_mode
for the brush would be nice).

Differential Revision: https://developer.blender.org/D16286

source/blender/blenkernel/intern/paint.cc

@@ -1043,6 +1043,8 @@ eObjectMode BKE_paint_object_mode_from_paintmode(ePaintMode mode)
       return OB_MODE_TEXTURE_PAINT;
     case PAINT_MODE_SCULPT_UV:
       return OB_MODE_EDIT;
+    case PAINT_MODE_SCULPT_CURVES:
+      return OB_MODE_SCULPT_CURVES;
     case PAINT_MODE_INVALID:
     default:
       return OB_MODE_OBJECT;