Fix an obsolete comment on a variable definition in expr.c.  No code changes.

FossilOrigin-Name: 012ff6dd306328f7ea71a6600471c871e7ffe37b
diff --git a/src/expr.c b/src/expr.c
index 31128cc..942b246 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -720,7 +720,7 @@
 ** is allocated to hold the integer text and the dequote flag is ignored.
 */
 Expr *sqlite3ExprAlloc(
-  sqlite3 *db,            /* Handle for sqlite3DbMallocZero() (may be null) */
+  sqlite3 *db,            /* Handle for sqlite3DbMallocRawNN() */
   int op,                 /* Expression opcode */
   const Token *pToken,    /* Token argument.  Might be NULL */
   int dequote             /* True to dequote */