Fixed a memory leak in an error path in the rule parser

Resolves: #69

Addresses:
```
Direct leak of 72 byte(s) in 1 object(s) allocated from:
    #0 0x7f8076950bb0 in operator new(unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc2bb0)
    #1 0x7f8075969fe5 in usbguard::parseRuleSpecification(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const*, unsigned int) src/Library/RuleParser.cpp:72
    #2 0x7f807599382f in usbguard::RulePrivate::fromString(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) src/Library/RulePrivate.cpp:599
    #3 0x7f8075958d38 in usbguard::Rule::fromString(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) src/Library/Rule.cpp:254
    #4 0x512764 in ____C_A_T_C_H____T_E_S_T____6 Regression/test_Rule_ghi37.cpp:15
    #5 0x461b26 in Catch::FreeFunctionTestCase::invoke() const (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x461b26)
    #6 0x416165 in Catch::TestCase::invoke() const ../../src/ThirdParty/Catch/include/internal/catch_test_case_info.hpp:176
    #7 0x45cffb in Catch::RunContext::invokeActiveTestCase() (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x45cffb)
    #8 0x45bcfe in Catch::RunContext::runCurrentTest(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x45bcfe)
    #9 0x454516 in Catch::RunContext::runTest(Catch::TestCase const&) (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x454516)
    #10 0x40d04f in Catch::runTests(Catch::Ptr<Catch::Config> const&) ../../src/ThirdParty/Catch/include/internal/../catch_session.hpp:78
    #11 0x45f67f in Catch::Session::run() (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x45f67f)
    #12 0x45ef2f in Catch::Session::run(int, char const* const*) (/home/james/deb-pkg/TEMP-PACKAGES/usbguard/upstream/src/Tests/.libs/lt-test-regression+0x45ef2f)
    #13 0x42ad3a in main ../../src/ThirdParty/Catch/include/internal/catch_default_main.hpp:15
    #14 0x7f80736df77f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2077f)
```

Author: Daniel Kopecek

src/Library/RuleParser.cpp

@@ -61,21 +61,27 @@ namespace usbguard
     try {
       RuleParserState state(rule_spec);
       quex::Lexer lexer(&stream);
-      quex::Token *token_ptr = nullptr;
+      QUEX_TYPE_TOKEN* token_ptr = nullptr;
 
 #ifndef NDEBUG
       RuleParserTrace(stderr, (char*)"RuleParser:");
 #endif
       for (;;) {
         lexer.receive(&token_ptr);
         if (token_ptr->type_id() != RULE_TOKEN_TERMINATION) {
-          RuleParser(parser_data.get(), token_ptr->type_id(), new QUEX_TYPE_TOKEN(*token_ptr), &state);
+          QUEX_TYPE_TOKEN* token_copy = new QUEX_TYPE_TOKEN(*token_ptr);
+          try {
+            RuleParser(parser_data.get(), token_ptr->type_id(), token_copy, &state);
+          }
+          catch(...) {
+            delete token_copy;
+            throw;
+          }
         } else {
           RuleParser(parser_data.get(), 0, nullptr, &state);
           break;
         }
       }
-
       return std::move(state.rule);
     }
     catch(RuleParserError& ex) {