8234841: Enhance buffering of byte buffers

Reviewed-by: alanb, ahgross, rhalade, psandoz

src/java.base/share/classes/java/nio/StringCharBuffer.java

@@ -43,12 +43,15 @@ class StringCharBuffer                                  // package-private
     }
 
     public CharBuffer slice() {
+        int pos = this.position();
+        int lim = this.limit();
+        int rem = (pos <= lim ? lim - pos : 0);
         return new StringCharBuffer(str,
                                     -1,
                                     0,
-                                    this.remaining(),
-                                    this.remaining(),
-                                    offset + this.position());
+                                    rem,
+                                    rem,
+                                    offset + pos);
     }
 
     @Override