closes #606 for Writer

Author: abumq

src/easylogging++.cc

@@ -2428,6 +2428,7 @@ Writer& Writer::construct(int count, const char* loggerIds, ...) {
     va_list loggersList;
     va_start(loggersList, loggerIds);
     const char* id = loggerIds;
+    m_loggerIds.reserve(count);
     for (int i = 0; i < count; ++i) {
       m_loggerIds.push_back(std::string(id));
       id = va_arg(loggersList, const char*);