Fix memzoom on Windows

Right now we can't call poll() on file and fifos on Windows. So we work
around that by simply blocking on keyboard input. This is OK because on
Windows we can't use /proc/*/mem for realtime monitoring, so there's no
reason not to block.

See #65

tool/viz/memzoom.c

@@ -318,6 +318,7 @@ static void PreventBufferbloat(void) {
 
 static bool HasPendingInput(void) {
   struct pollfd fds[1];
+  if (IsWindows()) return true; /* XXX */
   fds[0].fd = 0;
   fds[0].events = POLLIN;
   fds[0].revents = 0;
@@ -841,16 +842,19 @@ static void RangesZoom(void) {
 }
 
 static void MemZoom(void) {
+  bool ok;
+  ok = false;
   do {
     if (action & RESIZED) {
       GetTtySize();
       SetupCanvas();
       action &= ~RESIZED;
     }
-    if (HasPendingInput()) {
+    if (ok && HasPendingInput()) {
       ReadKeyboard();
-      continue;
+      if (!IsWindows()) continue; /* XXX */
     }
+    ok = true;
     if (pid) {
       RangesZoom();
     } else {