Double free (?) in VFS code

[cole-miller]

I'm opening this issue to track an integration test failure that I'm seeing on my local machine, but that evidently doesn't manifest on GHA or Launchpad. The test in question is vfs/changePageSize, introduced in #398, and I'm seeing a warning message from inside glibc (munmap_chunk(): invalid pointer), followed by a fatal SIGABRT. Based on GDB, the call stack looks like

sqlite3_free
sqlite3Pragma
sqlite3Parser
sqlite3RunParser
sqlite3_prepare_v2
sqlite3_exec

I haven't figured out how to get ASAN to diagnose what's happening -- it sees an illegal access (that occurs before whatever's causing the SIGABRT, I believe), but I can't tell where the memory in question was allocated. I don't know why this seemingly only happens on my machine, but hopefully we can figure it out once I understand what's causing the problem.