fixup! Bug 10760: Integrate TorButton to TorBrowser core

Bug 40501: High CPU load after tor exits unexpectedly

When a peers (tor) disconnects, Firefox seems to keep the stream open,
and return 0 on available, rather than throwing.
So, as a matter of fact, we had a while trying to read 0 bytes without
any pause in _readLine, hence the 100% CPU usage.

toolkit/torbutton/modules/tor-control-port.js

@@ -135,6 +135,18 @@ class AsyncSocket {
       this.inputQueue.push({
         onInputStreamReady: stream => {
           try {
+            if (!this.scriptableInputStream.available()) {
+              // This means EOF, but not closed yet. However, arriving at EOF
+              // should be an error condition for us, since we are in a socket,
+              // and EOF should mean peer disconnected.
+              // If the stream has been closed, this function itself should
+              // throw.
+              reject(
+                new Error("onInputStreamReady called without available bytes.")
+              );
+              return;
+            }
+
             // read our string from input stream
             let str = this.scriptableInputStream.read(
               this.scriptableInputStream.available()