Fix the domain matching method of the mix-list matcher.

[LEXUGE]

Currently, domain:le.com using mix-list method would cause www.google.com to match, which is unintended.
Also, currently the implementation causes le.com to fail matching domain:le.com as it is written as idx>0.

This fixes the aforementioned two issues.

Tested on my machine.

[codecov]

Codecov Report

Merging #246 into master will decrease coverage by 3.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #246      +/-   ##
==========================================
- Coverage   55.97%   52.72%   -3.26%     
==========================================
  Files          13       13              
  Lines         661      569      -92     
==========================================
- Hits          370      300      -70     
+ Misses        241      220      -21     
+ Partials       50       49       -1     

Impacted Files	Coverage Δ
core/outbound/clients/resolver/udp_resolver.go	60.00% <0.00%> (-11.43%)	⬇️
core/outbound/clients/resolver/tcp_resolver.go	25.00% <0.00%> (-8.34%)	⬇️
core/outbound/clients/resolver/tcptls_resolver.go	38.70% <0.00%> (-7.01%)	⬇️
core/outbound/dispatcher.go	52.87% <0.00%> (-4.42%)	⬇️
core/hosts/hosts.go	64.40% <0.00%> (-3.71%)	⬇️
core/outbound/clients/resolver/base_resolver.go	36.95% <0.00%> (-3.24%)	⬇️
core/outbound/clients/resolver/https_resolver.go	65.21% <0.00%> (-2.79%)	⬇️
core/outbound/clients/resolver/address.go	79.66% <0.00%> (-2.70%)	⬇️
core/common/ipset.go	91.42% <0.00%> (-1.52%)	⬇️
core/matcher/suffix/tree.go	86.48% <0.00%> (-0.75%)	⬇️
... and 3 more

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[shawn1m]

Merged. Thanks!