Stop ExtendedMessageFormat seekNonWs reading past the pattern end

[dxbjavid]

The registry-based ExtendedMessageFormat constructor parses its pattern with seekNonWs, which asks the split matcher about the character at the current parse index without first checking it is still inside the buffer. A truncated format element such as {, {0, or trailing text like {0}extra{ leaves the parse position at the end of the pattern, so the matcher reads one past the char array and the constructor throws ArrayIndexOutOfBoundsException rather than the documented IllegalArgumentException that the plain constructor already gives for the same input. This bounds the seek to the pattern length so those patterns report the usual unterminated-format-element error; a regression test covers the three shapes above.

[garydgregory]

@dxbjavid
Thank you for the PR, merged 🚀 Would you please port to Apache Commons Lang? See the assertions I added in 742fac0 post merge.

[dxbjavid]

sounds good, i'll port it across to commons-lang. its text.ExtendedMessageFormat carries the same seekNonWs helper, so the bounds fix and the truncated-element tests should move over cleanly, and i'll fold in the JRE sanity checks you added. will raise that separately.

[dxbjavid]

ported to commons-lang in apache/commons-lang#1740 - same seekNonWs bounds fix, the three truncated shapes and the JRE sanity checks all carried over.