patch 8.2.3246: memory use after free

Problem:    Memory use after free.
Solution:   When clearing a string option set the pointer to "empty_option".

Author: brammool

src/option.c

@@ -807,7 +807,7 @@ free_all_options(void)
 	else if (options[i].var != VAR_WIN
 		&& (options[i].flags & P_STRING))
 	    // buffer-local option: free global value
-	    free_string_option(*(char_u **)options[i].var);
+	    clear_string_option((char_u **)options[i].var);
     }
 }
 #endif

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3246,
 /**/
     3245,
 /**/