Fix a potential use-after-free following an OOM in sqlite3ParserAddCleanup()

and add a mechanism to detect situations where this might occur in the
future.

FossilOrigin-Name: 38ef8ab9830e12acd2c710e113939b1f8dced02612c6933c37a3c948a4030d0a

src/sqliteInt.h

@@ -3390,6 +3390,9 @@ struct Parse {
   u8 okConstFactor;    /* OK to factor out constants */
   u8 disableLookaside; /* Number of times lookaside has been disabled */
   u8 disableVtab;      /* Disable all virtual tables for this parse */
+#if defined(SQLITE_DEBUG) || defined(SQLITE_COVERAGE_TEST)
+  u8 earlyCleanup;     /* OOM inside sqlite3ParserAddCleanup() */
+#endif
   int nRangeReg;       /* Size of the temporary register block */
   int iRangeReg;       /* First register in temporary register block */
   int nErr;            /* Number of errors seen */