gutenprint: Fix ASSERT expression

Change-Id: I7fb39364fe8cf2b5596764bb4db3bda12295a171
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4096
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>
Reviewed-by: Jacob Secunda <secundaja@gmail.com>

src/add-ons/print/drivers/gutenprint/GPArray.cpp

@@ -32,7 +32,7 @@ template<typename TYPE>
 void
 GPArray<TYPE>::SetSize(int size)
 {
-	ASSERT(fSize == NULL);
+	ASSERT(fSize == 0);
 	fArray = new PointerType[size];
 	if (fArray == NULL)
 		return;