Check for and allow null critical sections, but log them.

stub XeKeysGetConsoleType
Removed the breakpoints in HandleCppException and RtlRaiseException until we have a real implementation of them. Some apps can continue fine afterwards.
Stub version of HalGetCurrentAVPack
Implement MmIsAddressValid
Implement RtlGetStackLimits

src/xenia/kernel/xboxkrnl/xboxkrnl_hal.cc

@@ -31,6 +31,13 @@ void HalReturnToFirmware_entry(dword_t routine) {
 }
 DECLARE_XBOXKRNL_EXPORT2(HalReturnToFirmware, kNone, kStub, kImportant);
 
+// this seems to be able to return a number of different values in the range 0
+// - 8. just returning four for now, because thats probably a better option than
+// returning whatever was in r3 to begin with
+dword_result_t HalGetCurrentAVPack_entry() { return 4; }
+
+DECLARE_XBOXKRNL_EXPORT1(HalGetCurrentAVPack, kNone, kStub);
+
 }  // namespace xboxkrnl
 }  // namespace kernel
 }  // namespace xe