Release the chunkBuffer if an exception is thrown whilst reading

If an exception was thrown due to an issue whilst reading the
MetricFamily into the slice, the buffer wasn't released and
Netty complained about ByteBuf being gc'ed without being explicitly
released.

Author: suhailpatel

common/src/main/java/com/zegelin/prometheus/exposition/JsonFormatChunkedInput.java

@@ -466,7 +466,12 @@ public ByteBuf readChunk(final ChannelHandlerContext ctx) throws Exception {
 
         // add slices till we hit the chunk size (or slightly over it), or hit EOF
         while (chunkBuffer.readableBytes() < 1024 * 1024 && state != State.EOF) {
-            nextSlice(chunkBuffer);
+            try {
+                nextSlice(chunkBuffer);
+            } catch (Exception e) {
+                chunkBuffer.release();
+                throw e;
+            }
         }
 
         return chunkBuffer;

common/src/main/java/com/zegelin/prometheus/exposition/TextFormatChunkedInput.java

@@ -359,8 +359,8 @@ public ByteBuf readChunk(final ChannelHandlerContext ctx) throws Exception {
         while (chunkBuffer.readableBytes() < 1024 * 1024 && state != State.EOF) {
             try {
                 nextSlice(chunkBuffer);
-
             } catch (Exception e) {
+                chunkBuffer.release();
                 throw e;
             }
         }