collect: respect stream pause / resume state

Without watching if a stream is already paused before calling pause(),
collect() can conflict with other users of the stream who may be
managing state, resulting in a premature collect().  This manifests in
the fstream-npm and node-tar combination where fstream-npm manages state
in readBundledLinks() at the same time collect() is processing the
stream. collect() ends up running before fstream-npm has properly set up
the _correct_ list of entries according to the ignore rules. When
collect() gets to run before this is complete, fstream starts performing
_read() operations on a non-filtered list, keeping track of entry index,
then after it starts, fstream-npm inserts a new list of entries and the
entry index is incorrect and can skip files.

Fixes: npm/npm#5082
Credit: @rvagg
Reviewed-By: @othiym23
PR-URL: #53

Author: rvagg

lib/collect.js

@@ -3,6 +3,8 @@ module.exports = collect
 function collect (stream) {
   if (stream._collected) return
 
+  if (stream._paused) return stream.on('resume', collect.bind(null, stream))
+
   stream._collected = true
   stream.pause()