all: misc updates

src/util/xspan_impl_common.h

@@ -113,6 +113,7 @@ forceinline ~CSelf() noexcept {}
 #endif
     noinline void invalidate() {
         assertInvariants();
+        // poison the pointer
         ptr = (pointer) (upx_uintptr_t) 16; // point to non-null invalid address
         // ptr = (pointer) (void *) &ptr; // point to self
         base = ptr;