Fix #119183: Use valid style for popup text size calculation

The current font style can be overridden with a input or other widget text style,
this change ensures that the right font style is set so `BLF_width` don't use a
overridden font text style.

Pull Request: https://projects.blender.org/blender/blender/pulls/119442

source/blender/windowmanager/intern/wm_operators.cc

@@ -1506,6 +1506,7 @@ static uiBlock *wm_block_dialog_create(bContext *C, ARegion *region, void *user_
 
   UI_block_flag_enable(block, UI_BLOCK_KEEP_OPEN | UI_BLOCK_NUMSELECT);
 
+  UI_fontstyle_set(&style->widget);
   /* Width based on the text lengths. */
   int text_width = std::max(
       120 * UI_SCALE_FAC,