compressor: fix memory leak in copy_stream()

The PyObject holding the result of the read() operation never
had its refcount decreased. This created a leak.

Fixes #40.

NEWS.rst

@@ -1,6 +1,11 @@
 Version History
 ===============
 
+0.8.2 (released 2018-02-22)
+---------------------------
+
+* Fixed memory leak in ``ZstdCompressor.copy_stream()`` (#40).
+
 0.8.1 (released 2017-04-08)
 ---------------------------
 

c-ext/compressor.c

@@ -313,7 +313,7 @@ static PyObject* ZstdCompressor_copy_stream(ZstdCompressor* self, PyObject* args
 	Py_ssize_t totalWrite = 0;
 	char* readBuffer;
 	Py_ssize_t readSize;
-	PyObject* readResult;
+	PyObject* readResult = NULL;
 	PyObject* res = NULL;
 	size_t zresult;
 	PyObject* writeResult;
@@ -410,6 +410,8 @@ static PyObject* ZstdCompressor_copy_stream(ZstdCompressor* self, PyObject* args
 				output.pos = 0;
 			}
 		}
+
+		Py_CLEAR(readResult);
 	}
 
 	/* We've finished reading. Now flush the compressor stream. */
@@ -455,6 +457,8 @@ static PyObject* ZstdCompressor_copy_stream(ZstdCompressor* self, PyObject* args
 		PyMem_Free(output.dst);
 	}
 
+	Py_XDECREF(readResult);
+
 	return res;
 }