Reset pointer to null after delete.

Fixes a double free.

Change-Id: Ieb71dff4476132b9b2fb624223e26af49a4131ee
Reviewed-on: https://swiftshader-review.googlesource.com/9728
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>

src/OpenGL/compiler/preprocessor/MacroExpander.cpp

diff --git a/src/OpenGL/compiler/preprocessor/MacroExpander.cpp b/src/OpenGL/compiler/preprocessor/MacroExpander.cpp
index d71562a..df0e495 100644
--- a/src/OpenGL/compiler/preprocessor/MacroExpander.cpp
+++ b/src/OpenGL/compiler/preprocessor/MacroExpander.cpp
@@ -154,6 +154,7 @@
 	{
 		*token = *mReserveToken;
 		delete mReserveToken;
+		mReserveToken = nullptr;
 		return;
 	}