enable p3dplugin.log by default too

direct/src/plugin_activex/PPLogger.cpp

@@ -126,6 +126,9 @@ void PPLogger::Open( const std::string &rootDir )
       log_basename = P3D_PLUGIN_LOG_BASENAME1;
     }
 #endif
+    if (log_basename.empty()) {
+      log_basename = "p3dplugin";
+    }
 
     if (!log_basename.empty()) {
       std::string log_pathname = log_directory;

direct/src/plugin_npapi/startup.cxx

@@ -79,6 +79,9 @@ open_logfile() {
       log_basename = P3D_PLUGIN_LOG_BASENAME1;
     }
 #endif
+    if (log_basename.empty()) {
+      log_basename = "p3dplugin";
+    }
 
     if (!log_basename.empty()) {
       string log_pathname = log_directory;