Fixed bug reported by Oracle QA team

GUI exist should call the other gui exist API with required arguments
Ldtp ldtp = new Ldtp("*Notepad");
ldtp.launchApp("notepad.exe");
System.out.println("status: " + ldtp.waitTillGuiExist());
System.out.println("result: " + ldtp.guiExist());

Thanks to Jia Liu <jia.jl.liu@oracle.com> for reporting the issue

QA Notes:
Testing Done: With the above test case provided by the Oracle team
Documentation Notes:
Bug Number:
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