Bug 1403185 - Fix button value index lookup oob for Windows Gamepads; r=ted

We can get button indexes in HID usage reports that do not actually
correspond to a button we store, meaning we can overstep bounds of the
button array. Check validity before accessing array.

MozReview-Commit-ID: AAQJLEgy2Ua

--HG--
extra : rebase_source : d665f7713612b76f7b36ca3d2ace1e6659bb5099

dom/gamepad/windows/WindowsGamepad.cpp

@@ -860,6 +860,11 @@ WindowsGamepadService::HandleRawInput(HRAWINPUT handle)
   memset(buttons.Elements(), 0, gamepad->numButtons * sizeof(bool));
 
   for (unsigned i = 0; i < usageLength; i++) {
+    // The button index in usages may be larger than what we detected when
+    // enumerating gamepads. If so, warn and continue.
+    if (NS_WARN_IF((usages[i] - 1) >= buttons.Length())) {
+      continue;
+    }
     buttons[usages[i] - 1] = true;
   }