Fix divide by zero crash in zone lighter

code/nel/src/3d/zone_lighter.cpp

@@ -1179,36 +1179,43 @@ void CZoneLighter::light (CLandscape &landscape, CZone& output, uint zoneToLight
 	// Set the thread state
 	_LastPatchComputed.resize (_ProcessCount);
 
+	if (patchCount)
+	{
 		// Launch threads
 		uint process;
-	for (process=0; process<_ProcessCount; process++)
+		for (process = 0; process < _ProcessCount; process++)
 		{
 			// Last patch
-		uint lastPatch=firstPatch+patchCountByThread;
+			uint lastPatch = firstPatch + patchCountByThread;
 			lastPatch %= patchCount;
 
 			// Last patch computed
 			_LastPatchComputed[process] = firstPatch;
 
 			// Create a thread
-		CLightRunnable *runnable = new CLightRunnable (process, this, &description);
-		IThread *pThread=IThread::create (runnable);
+			CLightRunnable *runnable = new CLightRunnable(process, this, &description);
+			IThread *pThread = IThread::create(runnable);
 			runnable->Thread = pThread;
 
 			// New first patch
-		firstPatch=lastPatch;
+			firstPatch = lastPatch;
 
 			// Launch
 			pThread->start();
 		}
 
 		// Wait for others processes
-	while (_ProcessExited!=_ProcessCount)
+		while (_ProcessExited != _ProcessCount)
 		{
-		nlSleep (1000);
+			nlSleep(1000);
 
 			// Call the progress callback
-		progress ("Lighting patches", (float)_NumberOfPatchComputed/(float)_PatchInfo.size());
+			progress("Lighting patches", (float)_NumberOfPatchComputed / (float)_PatchInfo.size());
+		}
+	}
+	else
+	{
+		nlwarning("Empty zone");
 	}
 
 	// Reset old thread mask