Fix incorrect column names in UPDATE statements generated by the sqldiff
utility.

FossilOrigin-Name: ee53b46011852e27db23708387fe1e918cc8284c
diff --git a/tool/sqldiff.c b/tool/sqldiff.c
index 28b66b2..53c5977 100644
--- a/tool/sqldiff.c
+++ b/tool/sqldiff.c
@@ -658,7 +658,7 @@
           zSep = " SET";
           for(i=nPk+1; i<nQ; i+=2){
             if( sqlite3_column_int(pStmt,i)==0 ) continue;
-            printf("%s %s=", zSep, az2[(i-1)/2]);
+            printf("%s %s=", zSep, az2[(i+nPk-1)/2]);
             zSep = ",";
             printQuoted(sqlite3_column_value(pStmt,i+1));
           }