In order to identify the first row of each partition, check if the rowid in the ephemeral table is 1 instead of using a dedicated flag register.

FossilOrigin-Name: f2d5f7a24c7aa483c579706c5bd7268a74da6d53025d78fa8642908c2aed1707

src/sqliteInt.h

@@ -3576,8 +3576,7 @@ struct Window {
   Expr *pOwner;           /* Expression object this window is attached to */
   int nBufferCol;         /* Number of columns in buffer table */
   int iArgCol;            /* Offset of first argument for this function */
-  int regFirst;
-
+  int regOne;             /* Register containing constant value 1 */
   int regStartRowid;
   int regEndRowid;
 };