Add test showing bug

Author: owen-mc

go/ql/test/query-tests/RedundantCode/UnreachableStatement/UnreachableStatement.expected

@@ -10,3 +10,4 @@
 | main.go:147:2:147:17 | return statement | This statement is unreachable. |
 | main.go:153:2:153:22 | return statement | This statement is unreachable. |
 | main.go:159:2:159:43 | return statement | This statement is unreachable. |
+| main.go:164:2:164:10 | select statement | This statement is unreachable. |

go/ql/test/query-tests/RedundantCode/UnreachableStatement/main.go

@@ -159,4 +159,9 @@ func test19() mystruct {
 	return mystruct{test10(1), test10(2) == 2} // $ Alert
 }
 
+func test20() {
+	go panic("panic in another goroutine")
+	select {} // $ SPURIOUS: Alert // reachable after starting the goroutine
+}
+
 func main() {}