fix(dehtml): do not insert unnecessary newlines when parsing <p> tags

Previously, parsing of `<p>Foo</p><p>Bar</p>`
resulted in `\n\nFoo\n\n\n\nBar\n\n`.

Now it results in `Foo\n\nBar`.

src/dehtml.rs

@@ -152,7 +152,7 @@ fn dehtml_endtag_cb(event: &BytesEnd, dehtml: &mut Dehtml) {
         .to_lowercase();
 
     match tag.as_str() {
-        "p" | "table" | "td" | "style" | "script" | "title" | "pre" => {
+        "style" | "script" | "title" | "pre" => {
             dehtml.strbuilder += &dehtml.append_prefix("\n\n");
             dehtml.add_text = AddText::YesRemoveLineEnds;
         }
@@ -200,7 +200,9 @@ fn dehtml_starttag_cb<B: std::io::BufRead>(
 
     match tag.as_str() {
         "p" | "table" | "td" => {
-            dehtml.strbuilder += &dehtml.append_prefix("\n\n");
+            if !dehtml.strbuilder.is_empty() {
+                dehtml.strbuilder += &dehtml.append_prefix("\n\n");
+            }
             dehtml.add_text = AddText::YesRemoveLineEnds;
         }
         #[rustfmt::skip]
@@ -353,6 +355,21 @@ mod tests {
         assert_eq!(plain, "line1\n\r\r\rline2\nline3");
     }
 
+    #[test]
+    fn test_dehtml_parse_p() {
+        let html = "<p>Foo</p><p>Bar</p>";
+        let plain = dehtml(html).unwrap();
+        assert_eq!(plain, "Foo\n\nBar");
+
+        let html = "<p>Foo<p>Bar";
+        let plain = dehtml(html).unwrap();
+        assert_eq!(plain, "Foo\n\nBar");
+
+        let html = "<p>Foo</p><p>Bar<p>Baz";
+        let plain = dehtml(html).unwrap();
+        assert_eq!(plain, "Foo\n\nBar\n\nBaz");
+    }
+
     #[test]
     fn test_dehtml_parse_href() {
         let html = "<a href=url>text</a";