fix return value of gethostby{name[2],addr} with no result but no error

commit f081d5336a80b68d3e1bed789cc373c5c3d6699b fixed
gethostbyname[2]_r to treat negative results as a non-error, leaving
gethostbyname[2] wrongly returning a pointer to the unfilled result
buffer rather than a null pointer. since, as documented with commit
fe82bb9b921be34370e6b71a1c6f062c20999ae0, the caller of
gethostby{name[2],addr}_r can always rely on the result pointer being
set, use that consistently rather than trying to duplicate logic about
whether we have a result or not in gethostby{name[2],addr}.

src/network/gethostbyaddr.c

@@ -20,5 +20,5 @@ struct hostent *gethostbyaddr(const void *a, socklen_t l, int af)
 		err = gethostbyaddr_r(a, l, af, h,
 			(void *)(h+1), size-sizeof *h, &res, &h_errno);
 	} while (err == ERANGE);
-	return err ? 0 : h;
+	return res;
 }

src/network/gethostbyname2.c

@@ -21,5 +21,5 @@ struct hostent *gethostbyname2(const char *name, int af)
 		err = gethostbyname2_r(name, af, h,
 			(void *)(h+1), size-sizeof *h, &res, &h_errno);
 	} while (err == ERANGE);
-	return err ? 0 : h;
+	return res;
 }