odd array subscript is above array bounds error

[Jack Howarth]

   While compiling the current pymol svn with gcc trunk
I ran across a compilation warning...

Ortho.c: In function 'OrthoFree':
Ortho.c:1973: warning: array subscript is above array bounds

which doesn't seem to make sense. The reduced test case that
triggers it with -O3 -Wall is...

#define CMD_QUEUE_MASK 0x3

void OrthoFree()
{

  typedef struct {
  char *ptr;
  unsigned int inp,out;
  unsigned int mask,size;
} CQueue;

   struct _COrtho {
   int X,Y,Height,Width;
   CQueue *cmdQueue[CMD_QUEUE_MASK+1];
  };
typedef struct _COrtho  COrtho;

    register COrtho *I=((void *)0);

    int a;

    for(a=0;a<=CMD_QUEUE_MASK;a++)
      ;
    I->cmdQueue[a] = ((void *)0);
}

which produces the warning...

test.c: In function ‘OrthoFree’:
test.c:24: warning: array subscript is above array bounds

...for the last assignment of I->cmdQueue[a] = ((void *)0).
It would seem to me that 'a' should be CMD_QUEUE_MASK+1
on exiting the for statement so that the assignment should
be valid. Thanks in advance for any feedback as to whether
I should open a PR for this against gcc trunk.
             Jack