RFR: JDK-8030179: java/nio/Buffer/Chars.java, testcases seems all pass but jtreg/testng failed with java.lang.AssertionError

[Xueming Shen]

Hi,

Please help review the fix for #8030179

issue: https://bugs.openjdk.java.net/browse/JDK-8030179
webrev: http://cr.openjdk.java.net/~sherman/8030179/webrev

This is the regression bug introduced in jdk7 when trying to optimize the single
byte encoding loop, in which the "optimization" code inappropriately updates the
"sl" (source limit) value and triggers misbehavior of the sgp parser (in which it
mistakenly returns "underflow" when it sees a high surrogate but can't see the next
low surrogate, because the "sl" is changed...)

Thanks!
-Sherman