win32u: Document the font_lock handling in font_EnumFonts().

dlls/win32u/font.c

@@ -3551,7 +3551,7 @@ static BOOL CDECL font_EnumFonts( PHYSDEV dev, LOGFONTW *lf, FONTENUMPROCW proc,
             {
                 if (!face_matches( family->family_name, face, face_name )) continue;
                 if (!enum_face_charsets( family, face, enum_charsets, count, proc, lparam, orig_name ))
-                    return FALSE;
+                    return FALSE; /* enum_face_charsets() unlocked font_lock */
 	    }
 	}
     }
@@ -3562,7 +3562,7 @@ static BOOL CDECL font_EnumFonts( PHYSDEV dev, LOGFONTW *lf, FONTENUMPROCW proc,
         {
             face = LIST_ENTRY( list_head(get_family_face_list(family)), struct gdi_font_face, entry );
             if (!enum_face_charsets( family, face, enum_charsets, count, proc, lparam, NULL ))
-                return FALSE;
+                return FALSE; /* enum_face_charsets() unlocked font_lock */
 	}
     }
     pthread_mutex_unlock( &font_lock );