Instead of directly calling stack_get, get the depth first and then call the maximum...

Instead of directly calling stack_get, get the depth first and then call the maximum depth

* Source/DebuggerConnection.m:
([DebuggerConnection updateStackTraceAndRegisters]): Call stack_depth which in turn calls stack_get
([DebuggerConnection _stackDepthReceived:]): Receives the depth of the stack and then asks for the stack at that depth