sequencer: stop pretending that an assignment is a condition

sequencer: stop pretending that an assignment is a condition

In 3e81bccdf3 (sequencer: factor out todo command name parsing,
2019-06-27), a `return` statement was introduced that basically was a
long sequence of conditions, combined with `&&`, except for the last
condition which is not really a condition but an assignment.

The point of this construct was to return 1 (i.e. `true`) from the
function if all of those conditions held true, and also assign the `bol`
pointer to the end of the parsed command.

Some static analyzers are really unhappy about such constructs. And
human readers are at least puzzled, if not confused, by seeing a single
`=` inside a chain of conditions where they would have expected to see
`==` instead and, based on experience, immediately suspect a typo.

Let's help all of this by turning this into the more verbose, more
readable form of an `if` construct that both assigns the pointer as well
as returns 1 if all of the conditions hold true.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>