Need to use preciseLength here to avoid too-short stream.

Author: headius

core/src/main/java/org/jruby/RubyString.java

@@ -5935,7 +5935,7 @@ else if (encidx == UTF32LEEncoding.INSTANCE) {
             }
 
             while (p < e) {
-                int ret = enc.length(pBytes, p, e);
+                int ret = StringSupport.preciseLength(enc, pBytes, p, e);
                 if (MBCLEN_NEEDMORE_P(ret)) {
                     break;
                 }