Update error message in writableSegment (#398)

Author: whyoleg

core/common/src/Buffer.kt

@@ -352,7 +352,9 @@ public class Buffer : Source, Sink {
     @PublishedApi
     @JvmSynthetic
     internal fun writableSegment(minimumCapacity: Int): Segment {
-        require(minimumCapacity >= 1 && minimumCapacity <= Segment.SIZE) { "unexpected capacity" }
+        require(minimumCapacity >= 1 && minimumCapacity <= Segment.SIZE) {
+            "unexpected capacity ($minimumCapacity), should be in range [1, ${Segment.SIZE}]"
+        }
 
         if (tail == null) {
             val result = SegmentPool.take() // Acquire a first segment.