Check for nil before using struct

[systay]

Fix for this problem:

I0529 01:54:58.175001    1272 logutil.go:31] log: http: panic serving 172.17.0.1:48142: runtime error: invalid memory address or nil pointer dereference
goroutine 26452 [running]:
net/http.(*conn).serve.func1(0xc0008aec80)
	/usr/local/go/src/net/http/server.go:1767 +0x139
panic(0x1e35d80, 0x3827060)
	/usr/local/go/src/runtime/panic.go:679 +0x1b2
vitess.io/vitess/go/vt/vttablet/tabletserver.txlogzHandler(0x25c8400, 0xc0005082a0, 0xc00010f800)
	/vt/src/vitess.io/vitess/go/vt/vttablet/tabletserver/txlogz.go:123 +0x368
net/http.HandlerFunc.ServeHTTP(0x22536f8, 0x25c8400, 0xc0005082a0, 0xc00010f800)
	/usr/local/go/src/net/http/server.go:2007 +0x44
net/http.(*ServeMux).ServeHTTP(0x3855320, 0x25c8400, 0xc0005082a0, 0xc00010f800)
	/usr/local/go/src/net/http/server.go:2387 +0x1bd
net/http.serverHandler.ServeHTTP(0xc0002321c0, 0x25c8400, 0xc0005082a0, 0xc00010f800)
	/usr/local/go/src/net/http/server.go:2802 +0xa4
net/http.(*conn).serve(0xc0008aec80, 0x25d4fc0, 0xc0009db980)
	/usr/local/go/src/net/http/server.go:1890 +0x875
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2928 +0x384

[teejae]

wanna do early return?

Suggested change

	if props != nil {
	if props == nil {
	continue

[deepthi]

LGTM.
Can merge once CI passes. I suggest squashing the commits since they are both small.

[deepthi]

If you don't mind, would you paste the reported error into the PR description so that future readers know what problem is being fixed?