Very little optimization by using a simpler scope_guard when possible

The version with the vector, that can be disabled etc, is “very” slow, so we
use unique_ptr when we don’t need to disable it, and when it only contains
one function

louloulibs/utils/encoding.cpp

@@ -76,7 +76,7 @@ namespace utils
   {
     // The given string MUST be a valid utf-8 string
     unsigned char* res = new unsigned char[original.size()];
-    ScopeGuard sg([&res]() { delete[] res;});
+    const auto sg = utils::make_scope_guard([&res](auto&&) { delete[] res;});
 
     // pointer where we write valid chars
     unsigned char* r = res;
@@ -140,7 +140,7 @@ namespace utils
         else
           throw std::runtime_error("Invalid UTF-8 passed to remove_invalid_xml_chars");
       }
-    return std::string(reinterpret_cast<char*>(res), r-res);
+    return {reinterpret_cast<char*>(res), static_cast<size_t>(r-res)};
   }
 
   std::string convert_to_utf8(const std::string& str, const char* charset)
@@ -152,7 +152,7 @@ namespace utils
       throw std::runtime_error("Cannot convert into UTF-8");
 
     // Make sure cd is always closed when we leave this function
-    ScopeGuard sg([&]{ iconv_close(cd); });
+    const auto sg = utils::make_scope_guard([&](auto&&){ iconv_close(cd); });
 
     size_t inbytesleft = str.size();
 
@@ -169,7 +169,7 @@ namespace utils
     char* outbuf_ptr = outbuf;
 
     // Make sure outbuf is always deleted when we leave this function
-    sg.add_callback([&]{ delete[] outbuf; });
+    const auto sg2 = utils::make_scope_guard([&](auto&&){ delete[] outbuf; });
 
     bool done = false;
     while (done == false)