Fix bug in StreamTransformer - ending fragment not getting sent (#2317)

* Fix bug in StreamTransformer - ending fragment not getting sent

* Add test to verify fix

Before:

```
> ChunkedStream / StreamTransformer
758 OK: output.moveString(s)
OUTPUT: 65 0d 0a 53 6f 6d 65 20 74 65 73 74 20 64 61 74  e..Some test dat
        61 0d 0a                                         a..
792 FAIL: FS_OUTPUT == s
FAIL in `virtual void StreamTest::execute()`
```

After:

```
>> ChunkedStream / StreamTransformer
741 OK: output.moveString(s)
OUTPUT: 65 0d 0a 53 6f 6d 65 20 74 65 73 74 20 64 61 74  e..Some test dat
        61 0d 0a 30 0d 0a 0d 0a                          a..0....
760 OK: FS_OUTPUT == s
```

Sming/Core/Data/Buffer/CircularBuffer.cpp

@@ -68,7 +68,7 @@ size_t CircularBuffer::room() const
 
 size_t CircularBuffer::write(uint8_t charToWrite)
 {
-	if(!room()) {
+	if(room() == 0) {
 		return 0;
 	}
 

Sming/Core/Data/StreamTransformer.cpp

@@ -37,7 +37,7 @@ void StreamTransformer::fillTempStream(char* buffer, size_t bufSize)
 	while((room = tempStream->room()) >= maxChunkSize) {
 		auto chunkSize = sourceStream->readMemoryBlock(buffer, maxChunkSize);
 		if(chunkSize == 0) {
-			return;
+			break;
 		}
 
 		saveState();
@@ -55,7 +55,9 @@ void StreamTransformer::fillTempStream(char* buffer, size_t bufSize)
 
 	if(sourceStream->isFinished()) {
 		auto outLength = transform(nullptr, 0, result, resultSize);
-		tempStream->write(result, outLength);
+		auto written = tempStream->write(result, outLength);
+		(void)written;
+		assert(written == outLength);
 	}
 }
 

tests/HostTests/modules/Stream.cpp

@@ -2,6 +2,7 @@
 #include <FlashString/TemplateStream.hpp>
 #include <Data/Stream/MemoryDataStream.h>
 #include <Data/Stream/Base64OutputStream.h>
+#include <Data/Stream/ChunkedStream.h>
 #include <Network/WebHelpers/base64.h>
 
 DEFINE_FSTR_LOCAL(template1, "Stream containing {var1}, {var2} and {var3}. {} {{}} {{12345")
@@ -86,6 +87,19 @@ class StreamTest : public TestGroup
 			REQUIRE(Resource::image_png == s);
 		}
 
+		TEST_CASE("ChunkedStream / StreamTransformer")
+		{
+			DEFINE_FSTR_LOCAL(FS_INPUT, "Some test data");
+			DEFINE_FSTR_LOCAL(FS_OUTPUT, "e\r\nSome test data\r\n0\r\n\r\n");
+			ChunkedStream chunked(new FlashMemoryStream(FS_INPUT));
+			MemoryDataStream output;
+			output.copyFrom(&chunked);
+			String s;
+			REQUIRE(output.moveString(s));
+			m_printHex("OUTPUT", s.c_str(), s.length());
+			REQUIRE(FS_OUTPUT == s);
+		}
+
 		TEST_CASE("MultipartStream / MultiStream")
 		{
 			unsigned itemIndex{0};