Fixed internal code bugs

Fixed a really obscure bug in the internal initconstants()
function of const.c that has been sitting for over 31 years!

    We are amazed that nobody has encountered this bug before
    now.  Nevertheless, our very extensive regression and
    multi-architecture testing found the bug.  Now, after all
    those years, it is fixed.

Fixed issues identied by the default CodeUL GitHub security code scan:

    Wrong type of arguments to printf in have_fpos_pos.c
    Multiplication result converted to larger type in zfunc.c

const.c

@@ -49,7 +49,7 @@ initconstants(void)
 		math_error("Unable to allocate constant table");
 		/*NOTREACHED*/
 	}
-	for (i = 0; consttable[i] != NULL; i++) {
+	for (i = 0; initnumbs[i] != NULL; i++) {
 		consttable[i] = initnumbs[i];
 	}
 	constcount = i-1;
@@ -123,6 +123,9 @@ addqconstant(NUMBER *q)
 	tp = consttable;
 	for (index = 0; index < constcount; index++, tp++) {
 		t = *tp;
+		if (t == NULL) {	/* paranoia */
+			break;
+		}
 		if (t->links == 0) {
 			if (!havefirst) {
 				havefirst = TRUE;