Fix GH-393 regression with mixed new line characters

src/ReverseMarkdown.Test/ConverterTests.Bug393_RegressionWithVaryingNewLines.verified.md

@@ -0,0 +1,7 @@
+This is regular text
+
+This is HTML: 
+
+* Line 1
+* Line 2
+* Line 3 has an unknown tag

src/ReverseMarkdown.Test/ConverterTests.cs

@@ -1376,5 +1376,13 @@ public Task Bug391_AnchorTagUnnecessarilyIndented()
 
             return CheckConversion(html, config);
         }
+
+        [Fact]
+        public Task Bug393_RegressionWithVaryingNewLines()
+        {
+            const string html = "This is regular text\r\n<p class=\"c1\">This is HTML: <ul><li>Line 1</li><li>Line 2</li><li><mark>Line 3 has an unknown tag</mark></li></ul></p>";
+            var config = new Config { UnknownTags = Config.UnknownTagsOption.Bypass, ListBulletChar = '*' };
+            return CheckConversion(html, config);
+        }
     }
 }

src/ReverseMarkdown.Test/ReverseMarkdown.Test.csproj

@@ -50,6 +50,9 @@
     </None>
     <None Update="ConverterTests.Bug391_AnchorTagUnnecessarilyIndented.verified.md">
       <DependentUpon>ConverterTests.WhenThereIsSingleAsteriskInText_ThenConvertToMarkdownEscapedAsterisk.verified.md</DependentUpon>
+    </None>
+    <None Update="ConverterTests.Bug393_RegressionWithVaryingNewLines.verified.md">
+      <DependentUpon>ConverterTests.WhenThereIsPreTag_ThenConvertToMarkdownPre.verified.md</DependentUpon>
     </None> 
   </ItemGroup>
 </Project>

src/ReverseMarkdown/StringUtils.cs

@@ -123,8 +123,8 @@ public static string EmphasizeContentWhitespaceGuard(this string content, string
 
         public static string FixMultipleNewlines(this string markdown)
         {
-            var normalizedMarkdown = Regex.Replace(markdown, @"\r\n|\r|\n", "\n");
-            var pattern = @"\n{2,}";
+            var normalizedMarkdown = Regex.Replace(markdown, @"\r\n|\r|\n", Environment.NewLine);
+            var pattern = $"{Environment.NewLine}{{2,}}";
             return Regex.Replace(normalizedMarkdown, pattern, Environment.NewLine + Environment.NewLine);
         }