i#1766: handle Chromium's _crtheap pointer being 1
i#1766: handle Chromium's _crtheap pointer being 1

Clamp any _crtheap pointer value that is a small integer to NULL to
work around problems stemming from Chromium's _crtheap being set to 1.

Fixes #1766

Review-URL: https://codereview.appspot.com/266950043

code4bones/drmemory,code4bones/drmemory,code4bones/drmemory,code4bones/drmemory,code4bones/drmemory