RFR: 8251499: no-placeholder compact number patterns throw IllegalArgumentException

[naoto.sato at oracle.com]

Hello,

Please review the fix for the following issue:

https://bugs.openjdk.java.net/browse/JDK-8251499

The proposed changeset is located at:

https://cr.openjdk.java.net/~naoto/8251499/webrev.00/

The current implementation of CompactNumberFormat assumes that there is 
always the number placeholder part in compact patterns. This is not 
always true. In fact, upcoming CLDR 38 resurrects such patterns, so this 
fix is a precursor to support CLDR 38.

Naoto