server_frontend_cert() crashes client

[predictiple]

version: 0.73.3
commit: 4a41ec1
build_time: "2024-12-05T19:15:42+02:00"
compiler: go1.23.2
system: linux
architecture: amd64

When given the query

SELECT server_frontend_cert() FROM scope()

the client crashes.

Backtrace:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x90 pc=0x1e24f48]

goroutine 269 [running]:
www.velocidex.com/golang/velociraptor/vql/server.(*ServerFrontendCertFunction).Call(0x2371280?, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840}, 0xc001cef180)
	/home/me/projects/velociraptor/vql/server/crypto.go:36 +0x208
www.velocidex.com/golang/vfilter.(*_SymbolRef).callFunction(0xc002030e00, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840}, {0x2baa540, 0x493fac0})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1795 +0x504
www.velocidex.com/golang/vfilter.(*_SymbolRef).Reduce(0xc002030e00, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1623 +0x52e
www.velocidex.com/golang/vfilter.(*_Value).Reduce(0xc002030e80, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1503 +0x13f
www.velocidex.com/golang/vfilter.(*_MemberExpression).Reduce(0xc001cee900, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1182 +0x45
www.velocidex.com/golang/vfilter.(*_MultiplicationExpression).Reduce(0xc001cee940, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1439 +0x3d
www.velocidex.com/golang/vfilter.(*_AdditionExpression).Reduce(0xc001cee980, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1354 +0x3d
www.velocidex.com/golang/vfilter.(*_ConditionOperand).Reduce(0xc002201470, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1392 +0x5a
www.velocidex.com/golang/vfilter.(*_OrExpression).Reduce(0xc001cee9c0, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1316 +0x45
www.velocidex.com/golang/vfilter.(*_AndExpression).Reduce(0xc001ceea40, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a840})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:1276 +0x45
www.velocidex.com/golang/vfilter.(*_AliasedExpression).Reduce(0x40?, {0x2bb84d0?, 0xc00210c5a0?}, {0x2c0d3a0?, 0xc00160a840?})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:712 +0x90
www.velocidex.com/golang/vfilter.(*_SelectExpression).Transform.func2({0x2bb84d0, 0xc00210c5a0}, {0xc000c82de0?, 0x16?})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:970 +0x55
www.velocidex.com/golang/vfilter.MaterializedLazyRow({0x2bb84d0, 0xc00210c5a0}, {0x242b0c0?, 0xc000281030}, {0x2c0d3a0, 0xc00160a780})
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/lazy.go:108 +0x1c7
www.velocidex.com/golang/vfilter.(*_Select).processSingleRow(0xc0021e1b60, {0x2bb84d0, 0xc00210c5a0}, {0x2c0d3a0, 0xc00160a6c0}, {0x2719f40, 0xc00160a6c0}, 0xc000fe9c00)
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:588 +0x145
www.velocidex.com/golang/vfilter.(*_Select).Eval.func3()
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:570 +0x13b
created by www.velocidex.com/golang/vfilter.(*_Select).Eval in goroutine 267
	/home/me/go/pkg/mod/www.velocidex.com/golang/[email protected]/vfilter.go:553 +0x295

[scudette]

Fixed by #3945