Do not accept a scaling factor of zero on PalmVNCSetScaleFactor and SetScale...

Do not accept a scaling factor of zero on PalmVNCSetScaleFactor and SetScale client->server messages. This would cause a division by zero and crash the server.

libvncserver/rfbserver.c

@@ -2491,6 +2491,13 @@ rfbProcessClientNormalMessage(rfbClientPtr cl)
           rfbCloseClient(cl);
           return;
       }
+
+      if (msg.ssc.scale == 0) {
+          rfbLogPerror("rfbProcessClientNormalMessage: will not accept a scale factor of zero");
+          rfbCloseClient(cl);
+          return;
+      }
+
       rfbStatRecordMessageRcvd(cl, msg.type, sz_rfbSetScaleMsg, sz_rfbSetScaleMsg);
       rfbLog("rfbSetScale(%d)\n", msg.ssc.scale);
       rfbScalingSetup(cl,cl->screen->width/msg.ssc.scale, cl->screen->height/msg.ssc.scale);
@@ -2507,6 +2514,13 @@ rfbProcessClientNormalMessage(rfbClientPtr cl)
           rfbCloseClient(cl);
           return;
       }
+
+      if (msg.ssc.scale == 0) {
+          rfbLogPerror("rfbProcessClientNormalMessage: will not accept a scale factor of zero");
+          rfbCloseClient(cl);
+          return;
+      }
+
       rfbStatRecordMessageRcvd(cl, msg.type, sz_rfbSetScaleMsg, sz_rfbSetScaleMsg);
       rfbLog("rfbSetScale(%d)\n", msg.ssc.scale);
       rfbScalingSetup(cl,cl->screen->width/msg.ssc.scale, cl->screen->height/msg.ssc.scale);