cmd/coordinator: fix sanity check

Change-Id: I2ba47f767f8213687b49e057a24d078c4512a5a2
Reviewed-on: https://go-review.googlesource.com/41373
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/cmd/coordinator/coordinator.go b/cmd/coordinator/coordinator.go
index 456261d..9ad7799 100644
--- a/cmd/coordinator/coordinator.go
+++ b/cmd/coordinator/coordinator.go
@@ -2581,7 +2581,7 @@
 	names := make([]string, len(tis))
 	for i, ti := range tis {
 		names[i] = ti.name
-		if i > 0 && !strings.HasPrefix(ti.name, "go_test:") {
+		if i > 0 && (!strings.HasPrefix(ti.name, "go_test:") || !strings.HasPrefix(names[0], "go_test:")) {
 			panic("only go_test:* tests may be merged")
 		}
 	}