[opengl] Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: Ia2f91707b277954d5105f6fdb489caad9ef8848c
diff --git a/opengl/tests/lib/glTestLib.cpp b/opengl/tests/lib/glTestLib.cpp
index 213dffd..290d7a0 100644
--- a/opengl/tests/lib/glTestLib.cpp
+++ b/opengl/tests/lib/glTestLib.cpp
@@ -37,7 +37,7 @@
 {
     const char *v = (const char *) glGetString(s);
 
-    if (v == NULL) {
+    if (v == nullptr) {
         testPrintI("GL %s unknown", name);
     } else {
         testPrintI("GL %s = %s", name, v);