cmd/coordinator: HTML escape another URL

This was missed from CL 179657.

Change-Id: I7e3966c1cd02f347b0f3ce96c13951b86a6a2b9b
Reviewed-on: https://go-review.googlesource.com/c/build/+/179697
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/cmd/coordinator/coordinator.go b/cmd/coordinator/coordinator.go
index ea5e411..1f289f2 100644
--- a/cmd/coordinator/coordinator.go
+++ b/cmd/coordinator/coordinator.go
@@ -3292,7 +3292,7 @@
 		text := evt.text
 		if htmlMode {
 			if e == "running_exec" {
-				e = fmt.Sprintf("<a href='%s'>%s</a>", st.logsURLLocked(), e)
+				e = fmt.Sprintf("<a href='%s'>%s</a>", html.EscapeString(st.logsURLLocked()), e)
 			}
 			e = "<b>" + e + "</b>"
 			text = "<i>" + html.EscapeString(text) + "</i>"