Fix #11966: Scrollbar may be incorrect on first opening of text file window. (#11981)

The scrollbar is set up before the true monospace is loaded, so reinitialise the window after loading.

src/textfile_gui.cpp

@@ -850,6 +850,9 @@ void TextfileWindow::LoadText(std::string_view buf)
 	this->AfterLoadText();
 
 	CheckForMissingGlyphs(true, this);
+
+	/* The font may have changed when searching for glyphs, so ensure widget sizes are updated just in case. */
+	this->ReInit();
 }
 
 /**