Handle idc.SetType return value correctly.

Apparently, idc.SetType returns True if the type is set for the first
time, False if the type is updated, and None if the type couldn't be set
(rather differently from what the documentation says).

Il2CppInspector.Common/Outputs/IDAPythonScript.cs

@@ -65,7 +65,7 @@ def MakeFunction(start):
 
 def SetType(addr, type):
   ret = idc.SetType(addr, type)
-  if ret == 0:
+  if ret is None:
     print('SetType(0x%x, %r) failed!' % (addr, type))
 ");