[Regression] Avoid locale-related conversion issues in editor

apps/opencs/model/prefs/state.cpp

@@ -3,6 +3,7 @@
 
 #include <stdexcept>
 #include <algorithm>
+#include <sstream>
 
 #include "intsetting.hpp"
 #include "doublesetting.hpp"
@@ -415,7 +416,9 @@ CSMPrefs::DoubleSetting& CSMPrefs::State::declareDouble (const std::string& key,
     if (mCurrentCategory==mCategories.end())
         throw std::logic_error ("no category for setting");
 
-    setDefault(key, std::to_string(default_));
+    std::ostringstream stream;
+    stream << default_;
+    setDefault(key, stream.str());
 
     default_ = mSettings.getFloat (key, mCurrentCategory->second.getKey());