ruleguard: move IsNil check above strings.Contains

Author: quasilyte

ruleguard/runner.go

@@ -387,10 +387,6 @@ func (rr *rulesRunner) renderMessage(msg string, m matchData, truncate bool) str
 
 	for _, c := range capture {
 		n := c.Node
-		key := "$" + c.Name
-		if !strings.Contains(msg, key) {
-			continue
-		}
 		// Some captured nodes are typed, but nil.
 		// We can't really get their text, so skip them here.
 		// For example, pattern `func $_() $results { $*_ }` may
@@ -399,6 +395,10 @@ func (rr *rulesRunner) renderMessage(msg string, m matchData, truncate bool) str
 		if reflect.ValueOf(n).IsNil() {
 			continue
 		}
+		key := "$" + c.Name
+		if !strings.Contains(msg, key) {
+			continue
+		}
 		buf.Reset()
 		buf.Write(rr.nodeText(n))
 		replacement := buf.String()