Reset bufpos to 0 immediately after refilling the buffer. Otherwise, we

Reset bufpos to 0 immediately after refilling the buffer.  Otherwise, we
risk leaving the connection in an indeterminate state if the server fails
to send a chunk delimiter.  Depending on the application and on the sizes
of the preceding chunks, the result can be anything from missing data to a
segfault.  With this patch, it will be reported as a protocol error.

PR:		204771
MFC after:	1 week