rebase -i: set commit to null in exec commands

Make sure commit is set to NULL when parsing exec instructions
from the todo list. If not, we may try to access an uninitialized
address later while updating the todo list.

Signed-off-by: Liam Beguin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: liambeguin

sequencer.c

@@ -1268,6 +1268,7 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	bol += padding;
 
 	if (item->command == TODO_EXEC) {
+		item->commit = NULL;
 		item->arg = bol;
 		item->arg_len = (int)(eol - bol);
 		return 0;