fpGUI minor code improvement suggestions

[deanm73]

These are small code improvements that might make the framework slightly more robust:

src/corelib/fpg_msgqueue.inc
procedure fpgInitMsgQueue;
after line "uMsgQueueList := TList.Create;"
add "uMsgQueueList.Capacity := cMessageQueueSize;"

procedure fpgDeliverMessage
replace "msg.Dest.Free"
with "FreeAndNil(msg.Dest)"

src/corelib/fpg_main.pas
procedure TfpgApplication.RunMessageLoop;
reduce timeout from "WaitWindowMessage(2000);"
to "WaitWindowMessage(100);"

src/corelib/fpg_widget.pas
procedure procedure TfpgWidget.MsgPaint
put code between "Canvas.BeginDraw;" and "Canvas.EndDraw" into try...finally