A better comment on the generated code for the NULL-in-RHS-of-IN detection
logic.

FossilOrigin-Name: 9bc1c730a366e75b760b58e7a343d39165b2a469
diff --git a/src/expr.c b/src/expr.c
index 6440dea..c32affe 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1476,8 +1476,8 @@
 }
 
 /*
-** Generate code that checks the single-column index table iCur to see if
-** contains any NULL entries.  Cause the register at regHasNull to be set
+** Generate code that checks the left-most column of index table iCur to see if
+** it contains any NULL entries.  Cause the register at regHasNull to be set
 ** to a non-NULL value if iCur contains no NULLs.  Cause register regHasNull
 ** to be set to NULL if iCur contains one or more NULL values.
 */
@@ -1487,7 +1487,7 @@
   j1 = sqlite3VdbeAddOp1(v, OP_Rewind, iCur); VdbeCoverage(v);
   sqlite3VdbeAddOp3(v, OP_Column, iCur, 0, regHasNull);
   sqlite3VdbeChangeP5(v, OPFLAG_TYPEOFARG);
-  VdbeComment((v, "<maybe-NULL?>"));
+  VdbeComment((v, "first_entry_in(%d)", iCur));
   sqlite3VdbeJumpHere(v, j1);
 }