chore: fix compiler warnings (#74)

Author: mfenniak

src/python.c

@@ -922,7 +922,7 @@ execute(ForeignScanState *node, ExplainState *es)
 	{
 		MulticornBaseQual *qual = lfirst(lc);
 		MulticornConstQual *newqual = NULL;
-		bool		isNull;
+		bool		isNull = false;
 		ExprState  *expr_state = NULL;
 
 		switch (qual->right_type)

src/query.c

@@ -67,7 +67,6 @@ extractColumns(List *reltargetlist, List *restrictinfolist)
 {
 	ListCell   *lc;
 	List	   *columns = NULL;
-	int			i = 0;
 
 	foreach(lc, reltargetlist)
 	{
@@ -76,7 +75,6 @@ extractColumns(List *reltargetlist, List *restrictinfolist)
 
 		targetcolumns = pull_var_clause(node, PVC_RECURSE_AGGREGATES| PVC_RECURSE_PLACEHOLDERS);
 		columns = list_union(columns, targetcolumns);
-		i++;
 	}
 	foreach(lc, restrictinfolist)
 	{
@@ -363,7 +361,7 @@ extractClauseFromOpExpr(
 		/* Do not add it if it either contains a mutable function, or makes */
 		/* self references in the right hand side. */
 		if (!(contain_volatile_functions((Node *) right) ||
-			  bms_is_subset(base_relids, 
+			  bms_is_subset(base_relids,
 					pull_varnos(
 #if PG_VERSION_NUM >= 140000
 											root,