[xml] Problem in case of Failure of xmlGetGlobalState

["ashwin sinha" <4shw1ns1nh4 gmail com>]

Hi, 
       
This is with reference to the xmlGetGlobalState function. If
this function returns NULL due to a failure in xmlNewGlobalState
function, then it will lead to a crash in functions like     __xmlBufferAllocScheme on the line
       return (&xmlGetGlobalState()->xmlBufferAllocScheme); 

  There are a number of functions like this in globals.c and all of them will have the same problem. 
    At first i thought having a check for the return value of
xmlGetGlobalState function would take care of the problem, but it will
not, because if we return NULL from there the macros defined in
globals.h would try to de-reference NULL pointers.

 So I am thinking we need to return a function pointer to a dummy
function(in case xmlGetGlobalState fails) which will always return NULL
in order to solve the problem. Is this the correct way to go about it,
or is there a better way? 

Thanks 
Ashwin