reporter: Fix io.EOF handling (#3010)

The way the if statement was written, if there is an io.EOF error, then
we still first try reading the response object, however, in the io.EOF
case it's null, therefore the if statement needs to be swapped around so
it would never try to read something on the nil pointer if an io.EOF
error is returned.

Author: brancz

reporter/parca_reporter.go

@@ -617,7 +617,7 @@ func (r *ParcaReporter) reportDataToBackend(ctx context.Context, buf *bytes.Buff
 	if err != nil && err != io.EOF {
 		return err
 	}
-	if len(resp.Record) == 0 || err == io.EOF {
+	if err == io.EOF || len(resp.Record) == 0 {
 		// The backend didn't want any more information.
 		return nil
 	}