Avoid constructing icu::StringPiece from std::string directly

Otherwise it causes a crash on Windows when OpenMW is built in debug
mode but ICU not.

components/l10n/messagebundles.cpp

@@ -75,7 +75,7 @@ namespace l10n
             {
                 const auto key = it.first.as<std::string>();
                 const auto value = it.second.as<std::string>();
-                icu::UnicodeString pattern = icu::UnicodeString::fromUTF8(value);
+                icu::UnicodeString pattern = icu::UnicodeString::fromUTF8(icu::StringPiece(value.data(), value.size()));
                 icu::ErrorCode status;
                 UParseError parseError;
                 icu::MessageFormat message(pattern, lang, parseError, status);
@@ -112,7 +112,7 @@ namespace l10n
         std::vector<icu::Formattable> argValues;
         for (auto& [k, v] : args)
         {
-            argNames.push_back(icu::UnicodeString::fromUTF8(k));
+            argNames.push_back(icu::UnicodeString::fromUTF8(icu::StringPiece(k.data(), k.size())));
             argValues.push_back(v);
         }
         return formatMessage(key, argNames, argValues);

components/lua/l10n.cpp

@@ -68,7 +68,8 @@ namespace LuaUtil
             }
 
             // Argument names
-            argNames.push_back(icu::UnicodeString::fromUTF8(key.as<std::string>()));
+            const auto str = key.as<std::string>();
+            argNames.push_back(icu::UnicodeString::fromUTF8(icu::StringPiece(str.data(), str.size())));
         }
         return std::make_pair(args, argNames);
     }