Fix misleading progress indicators with zero ticks

[nickbeen]

What does this pull request do?

This PR fixes misleading progress indicators when both progress and maxProgress are equal to zero. Originally both values would reset to one to avoid a DivisionByZero error (#22).

Fixes #25

Why is this pull request needed?

This new behavior will show the correct progress values in situations where a programmatic loop has nothing to tick through.

This PR will be released within a new minor version since it changes to behavior of progress and maxProgress for anyone who explicitly checks these values in their code.

$progressBar = new ProgressBar(progress: 0, maxProgress: 0);
$progressBar->start();

while ($i <= 10) {
  continue; /* nothing to tick */
}

$progressBar->finish();

/* previous behavior */
1/1 [############################] 100% 

/* new behavior */
0/0 [############################] 100% 

How does this pull request work?

Values for progress and maxProgress no longer reset to one when both values are zero by default. When both values are zero, the percentage is automatically set to 100% without any calculation to avoid a DivisionByZero error.