Fix the B2C converter.

Fix the B2C converter.
Sometimes data comes in incomplete chunks, and we have to check to see if we have available data, otherwise, when we return -1, the underlying InputStreamReader actually returns 1, and we get garbage in the output data.
I will discuss this on the dev list, since it affects all tomcat versions, at that time I will also provide a test case showing what can happen. Please comment on this fix, if there is something alarming

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@568307 13f79535-47bb-0310-9956-ffa450edef68