Check length of BaseResolvers to prevent division by zero

[sausagenoods]

I noticed that when nuclei is supplied with an empty resolver list file (-r option), it panics:

panic: runtime error: integer divide by zero

goroutine 112869 [running]:
github.com/projectdiscovery/retryabledns.(*Client).Do(0xc0038e2c80, 0x1?)
	/root/go/pkg/mod/github.com/projectdiscovery/retryabledns@v1.0.20/client.go:113 +0x2ee
github.com/projectdiscovery/nuclei/v2/pkg/protocols/dns.(*Request).ExecuteWithResults(0xc000040f00, 0xc0040c7f80, 0xc00406fc50, 0x7fcd0cf4bf18?, 0xc003932198)
	/root/go/pkg/mod/github.com/projectdiscovery/nuclei/v2@v2.8.9/pkg/protocols/dns/request.go:93 +0x79c
github.com/projectdiscovery/nuclei/v2/pkg/templates.(*ClusterExecuter).Execute(0xc004ec4a80, 0xc0040c7f00)
	/root/go/pkg/mod/github.com/projectdiscovery/nuclei/v2@v2.8.9/pkg/templates/cluster.go:245 +0x22d
github.com/projectdiscovery/nuclei/v2/pkg/core.(*Engine).executeTemplateWithTargets.func2.1(0x76c406?, 0x0?, 0xc0040c7d00)
	/root/go/pkg/mod/github.com/projectdiscovery/nuclei/v2@v2.8.9/pkg/core/executors.go:130 +0x296
created by github.com/projectdiscovery/nuclei/v2/pkg/core.(*Engine).executeTemplateWithTargets.func2
	/root/go/pkg/mod/github.com/projectdiscovery/nuclei/v2@v2.8.9/pkg/core/executors.go:107 +0x4f8

The panic is caused by this line: https://github.com/projectdiscovery/retryabledns/blob/main/client.go#L113
Modulo operator is ran with 0 when c.resolvers is empty.

I added a check for BaseResolvers' length to prevent it from panicking.

Related - projectdiscovery/nuclei#2515

[Mzack9999]

Nice catch - Thanks for the PR @sausagenoods !