try to satisfy msrv?

src/book/summary.rs

@@ -374,11 +374,13 @@ impl<'a> SummaryParser<'a> {
 
         loop {
             match self.next_event() {
-                Some(ev @ Event::Start(Tag::Paragraph)) if !first => {
+                Some(ev @ Event::Start(Tag::Paragraph)) => {
+                    if !first {
                         // we're starting the suffix chapters
                         self.back(ev);
                         break;
                     }
+                }
                 // The expectation is that pulldown cmark will terminate a paragraph before a new
                 // heading, so we can always count on this to return without skipping headings.
                 Some(ev @ Event::Start(Tag::Heading(1))) => {