Allow @exclusive variables with gaps between @inner loops

[dmed256]

The exclusive index variable increments in the inner-most @inner loop and is reset to 0 in the inner-most @outer-loop

In reality, we should be resetting the index in the @inner loops

const int _occa_prev_exclusive_index = _occa_exclusive_index;
for (...; @inner) { 
  ...
  ++_occa_exclusive_index;
}
_occa_exclusive_index = _occa_prev_exclusive_index;