Refactoring: replace NULL by nullptr for pointers (2nd CL).

This CL mainly handles the pointer comparisons (== or !=).

BUG=angleproject:2001

Change-Id: I25ac3b61032e7ad91459a1c6541cadc87cf9b160
Reviewed-on: https://chromium-review.googlesource.com/483935
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 22973eb..348f4ad 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -4099,7 +4099,7 @@
     {
         gl::Texture *tex = context->getTexture(texture);
 
-        if (tex == NULL)
+        if (tex == nullptr)
         {
             context->handleError(Error(GL_INVALID_OPERATION));
             return false;