conv: prevent StripHtmlTags from falling into infinite loop

malformed tags could cause this, e.g. ../span><br>..,
position of < would be the same as >, nothing would be actually
removed and the operation would be performed ad infinitum.

src/conv.cpp

@@ -279,7 +279,7 @@ void StripHtmlTags(std::string &s)
 	bool erase = 0;
 	for (size_t i = s.find("<"); i != std::string::npos; i = s.find("<"))
 	{
-		size_t j = s.find(">")+1;
+		size_t j = s.find(">", i)+1;
 		s.replace(i, j-i, "");
 	}
 	Replace(s, "&#039;", "'");