Possible out_of_range exception for millisecond formats in CachedDateFormat

In 2010 we recognized what I think is a bug in CachedDateFormat::findMillisecondStart which leads to out_of_range exceptions depending on the time when log statements were issued. We always log with milliseconds enabled and the mentioned method seems to incorrectly assume it always needs to compare 3 characters. The following lines are some debug output made those days for a working log statement:

ConversionPattern %d

formatted[i] 2010-08-12 11:04:50,406
plusMagic[i] 2010-08-12 11:04:50,654
plusZero 2010-08-12 11:04:50,000
plusZero.length() 23
formatted.length() 23
i 20
magicString 654
formattedMillis 406
zeroString ""

i is 20 and we have 3 characters for milliseconds to compare, therefore no problem. Next the output for a statement where the execeptions got thrown:

ConversionPattern %d

formatted[i] 2010-08-12 11:04:50,609
plusMagic[i] 2010-08-12 11:04:50,654
plusZero 2010-08-12 11:04:50,000
plusZero.length() 23
formatted.length() 23
i 21
magicString 654
formattedMillis 609
zeroString ""

Now i is 21 because the first characters of the milliseconds are equal, therefore we can't compare additional 3 characters, but only 2.