don't imbue boost::filesystem::path with locale "C" on windows

fixes bitcoin#6078

Github-Pull: bitcoin#6093
Rebased-From: b3ffcdf 3da7849
(cherry picked from commit 424ae66)

src/util.cpp

@@ -713,18 +713,20 @@ void RenameThread(const char* name)
 
 void SetupEnvironment()
 {
-    std::locale loc("C");
     // On most POSIX systems (e.g. Linux, but not BSD) the environment's locale
     // may be invalid, in which case the "C" locale is used as fallback.
 #if !defined(WIN32) && !defined(MAC_OSX) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
     try {
-        loc = std::locale(""); // Raises a runtime error if current locale is invalid
+        std::locale(""); // Raises a runtime error if current locale is invalid
     } catch (const std::runtime_error&) {
         setenv("LC_ALL", "C", 1);
     }
 #endif
-    // The path locale is lazy initialized and to avoid deinitialization errors 
+    // The path locale is lazy initialized and to avoid deinitialization errors
     // in multithreading environments, it is set explicitly by the main thread.
+    // A dummy locale is used to extract the internal default locale, used by
+    // boost::filesystem::path, which is then used to explicitly imbue the path.
+    std::locale loc = boost::filesystem::path::imbue(std::locale::classic());
     boost::filesystem::path::imbue(loc);
 }