Make sure the given display is a valid pointer. EGL functions are supposed to return EGL_BAD_DISPLAY when the display is an invalid pointer. Since there is very rarely more than one simultaneous display, iterating through the map is not costly. BUG=angleproject:970 Change-Id: I3d9b842a49c5c99f9b8fad3d7ef53f9f5d3057ba Reviewed-on: https://chromium-review.googlesource.com/287342 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>