32-bit malloc_callstacks nondet failure: extra invalid heap error 0xbcbcbcbc x2116

This happened once in the maybe dozen runs of the x86 job I've done on GA CI on Ubuntu20.
Locally I get 8 unique, 10 total invalid heap arguments and don't see this weird (DR heap padding pattern?) 0xbcbcbcbc:

```
~~Dr.M~~ 9 unique, 2126 total invalid heap argument(s)

34: DUPLICATE ERROR COUNTS:
34: Error # 6: 2
34: Error # 7: 2
34: Error # 10: 2116

34: Error #10: INVALID HEAP ARGUMENT to free 0xbcbcbcbc
34: # 0 replace_operator_delete_array (0x738c10e3 )
34: /home/runner/work/drmemory/drmemory/common/alloc_replace.c:3002
34: # 1 hasdtr::~hasdtr (0xf3b1d53a )
34: /home/runner/work/drmemory/drmemory/tests/cs2bug.cpp:116
34: # 2 test_mismatch_dtr (0xf3b1d08b )
34: /home/runner/work/drmemory/drmemory/tests/cs2bug.cpp:206
34: # 3 main (0xf3b1d3f8 )
34: /home/runner/work/drmemory/drmemory/tests/cs2bug.cpp:247
34: Note: @0:00:01.422 in thread 31565
```