Prevent undefined offset when formatBitrate is given a significantly large enough...

Prevent undefined offset when formatBitrate is given a significantly large enough number (10^27)

> echo $wgLang->formatBitrate( pow( 10, 27 ) );
PHP Notice:  Undefined offset: 9 in /home/reedy/mediawiki/trunk/phase3/languages/Language.php on line 3827
PHP Stack trace:
PHP   1. {main}() /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php:0
PHP   2. eval() /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php:82
PHP   3. Language->formatBitrate() /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php(82) : eval()'d code:1

Notice: Undefined offset: 9 in /home/reedy/mediawiki/trunk/phase3/languages/Language.php on line 3827

Call Stack:
    0.0006     650736   1. {main}() /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php:0
   61.6539   21593432   2. eval(''echo $wgLang->formatBitrate( pow( 10, 27 ) );;'') /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php:82
   61.6540   21593512   3. Language->formatBitrate() /home/reedy/mediawiki/trunk/phase3/maintenance/eval.php(82) : eval()'d code:1

1bps