[SLOF] Compiler warnings

[Adrian Reber]

With gcc 6.1.1 I see two compiler warnings which I am not sure how to
solve:

	[CC]	paflof.o
/tmp/SLOF/slof/paflof.c: In function ‘engine’:
/tmp/SLOF/slof/paflof.c:83:23: warning: array subscript is below array bounds [-Warray-bounds]
   dp = the_data_stack - 1;
        ~~~~~~~~~~~~~~~^~~
/tmp/SLOF/slof/paflof.c:84:22: warning: array subscript is below array bounds [-Warray-bounds]
   rp = handler_stack - 1;
        ~~~~~~~~~~~~~~^~~

		Adrian