Core/Logging: Fixed a possible crash with dynamic log file names

src/server/shared/Logging/Appender.h

@@ -139,7 +139,7 @@ class Appender
         static const char* getLogFilterTypeString(LogFilterType type);
 
     private:
-        virtual void _write(LogMessage& /*message*/) {};
+        virtual void _write(LogMessage& /*message*/) = 0;
 
         uint8 id;
         std::string name;

src/server/shared/Logging/AppenderFile.cpp

@@ -26,7 +26,7 @@ AppenderFile::AppenderFile(uint8 id, std::string const& name, LogLevel level, co
 {
     dynamicName = std::string::npos != filename.find("%u");
     backup = _flags & APPENDER_FLAGS_MAKE_FILE_BACKUP;
-    
+
     logfile = !dynamicName ? OpenFile(_filename, _mode, backup) : NULL;
 }
 
@@ -54,7 +54,10 @@ void AppenderFile::_write(LogMessage& message)
         fflush(logfile);
 
         if (dynamicName)
+        {
             fclose(logfile);
+            logfile = NULL;
+        }
     }
 }