parser: fix regex parser leak on parsing failure

When the regex parser failed, the Chars objects created/used in rules
charset and cset_chars would not be cleaned up properly and would
leak.

Closes #361

Signed-off-by: Georgia Garcia <georgia.garcia@canonical.com>

parser/libapparmor_re/parse.y

@@ -72,6 +72,7 @@ static inline Chars* insert_char_range(Chars* cset, transchar a, transchar b)
  * parsing succeeds!
  */
 %destructor { $$->release(); } expr terms0 terms qterm term
+%destructor { delete $$; } charset cset_chars
 
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