Markdown: fix the condition to detect code blocks

Units/parser-markdown.r/code-block-under-items.d/args.ctags

@@ -0,0 +1,3 @@
+--sort=no
+--extras=+g
+--fields=+{language}

Units/parser-markdown.r/code-block-under-items.d/expected.tags

@@ -0,0 +1,10 @@
+test	input.md	/^# test$/;"	c	language:Markdown
+department2	input.md	/^  create table department2($/;"	t	language:SQL
+id	input.md	/^      id int primary key,$/;"	E	language:SQL	table:department2
+name	input.md	/^      name varchar(20),$/;"	E	language:SQL	table:department2
+comment	input.md	/^      comment varchar(100)$/;"	E	language:SQL	table:department2
+department3	input.md	/^  create table department3($/;"	t	language:SQL
+id	input.md	/^      id int,$/;"	E	language:SQL	table:department3
+name	input.md	/^      name varchar(20),$/;"	E	language:SQL	table:department3
+comment	input.md	/^      comment varchar(100),$/;"	E	language:SQL	table:department3
+foo	input.md	/^  foo()$/;"	f	language:Sh

Units/parser-markdown.r/code-block-under-items.d/input.md

@@ -0,0 +1,29 @@
+<!-- Taken from #3625 submitted by @jiz4oh -->
+# test
+
+- primary key：
+
+  ```sql
+  # method 1
+  create table department2(
+      id int primary key,
+      name varchar(20),
+      comment varchar(100)
+      );
+
+  # method 2
+  create table department3(
+      id int,
+      name varchar(20),
+      comment varchar(100),
+      constraint pk_name primary key(id); 
+  ```
+
+- second key:
+
+  ```sh
+  foo()
+  {
+	  :
+  }
+  ```

parsers/markdown.c

@@ -283,7 +283,7 @@ static void findMarkdownTags (void)
 			char c = line[pos];
 			char otherC = c == '`' ? '~' : '`';
 			int nSame;
-			for (nSame = 1; line[nSame] == line[pos]; ++nSame);
+			for (nSame = 1; line[nSame + pos] == line[pos]; ++nSame);
 
 			if (inCodeChar != otherC && nSame >= 3)
 			{