[gh 17847] data->pos_delta should stick at infinity

The expression we're about to add to data->pos_delta in this part of
study_chunk() can be both positive or negative; however while we apply
an overflow check to avoid exceeding OPTIMIZE_INFTY, we were happily
subtracting from it when the expression was negative, making it no longer
infinite.

regcomp.c

@@ -5842,6 +5842,7 @@ Perl_re_printf( aTHX_  "LHS=%" UVuf " RHS=%" UVuf "\n",
           - minnext * mincount), (UV)(OPTIMIZE_INFTY - data->pos_delta));
 #endif
 		    if (deltanext == OPTIMIZE_INFTY
+                        || data->pos_delta == OPTIMIZE_INFTY
                         || -counted * deltanext + (minnext + deltanext) * maxcount - minnext * mincount >= OPTIMIZE_INFTY - data->pos_delta)
 		        data->pos_delta = OPTIMIZE_INFTY;
 		    else