lib: remove and restructure calls to isNaN()

Switch condition order to check for null before calling isNaN().
Also remove two unnecessary calls to isNaN() that are already
covered by calls to isFinite(). This commit targets v0.10, as
opposed to #7891, which targets master (suggested by
@bnoordhuis). Closes #7840.

Signed-off-by: Fedor Indutny <fedor@indutny.com>

lib/_stream_readable.js

@@ -218,7 +218,7 @@ function howMuchToRead(n, state) {
   if (state.objectMode)
     return n === 0 ? 0 : 1;
 
-  if (isNaN(n) || n === null) {
+  if (n === null || isNaN(n)) {
     // only flow one buffer at a time
     if (state.flowing && state.buffer.length)
       return state.buffer[0].length;

lib/assert.js

@@ -54,7 +54,7 @@ function replacer(key, value) {
   if (value === undefined) {
     return '' + value;
   }
-  if (typeof value === 'number' && (isNaN(value) || !isFinite(value))) {
+  if (typeof value === 'number' && !isFinite(value)) {
     return value.toString();
   }
   if (typeof value === 'function' || value instanceof RegExp) {

lib/net.js

@@ -306,7 +306,7 @@ Socket.prototype.listen = function() {
 
 
 Socket.prototype.setTimeout = function(msecs, callback) {
-  if (msecs > 0 && !isNaN(msecs) && isFinite(msecs)) {
+  if (msecs > 0 && isFinite(msecs)) {
     timers.enroll(this, msecs);
     timers._unrefActive(this);
     if (callback) {