Don't set Content-Type unless specified
Don't set Content-Type unless specified

Otherwise this might segfault

Change-Id: I82d391f15ab2fa006a6b1311d8ed8379742d8d79
Reviewed-on: http://review.couchbase.org/41946
Tested-by: Mark Nunberg <e7d42768707bf23038325b0b68d4b577e5f6064a@haskalah.org>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

couchbase/libcouchbase,avsej/libcouchbase,maxim-ky/libcouchbase,senthilkumaranb/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,kojiromike/libcouchbase,senthilkumaranb/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,kojiromike/libcouchbase,maxim-ky/libcouchbase,signmotion/libcouchbase,avsej/libcouchbase,signmotion/libcouchbase,couchbase/libcouchbase,mnunberg/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,couchbase/libcouchbase,signmotion/libcouchbase,avsej/libcouchbase,signmotion/libcouchbase,maxim-ky/libcouchbase,maxim-ky/libcouchbase,senthilkumaranb/libcouchbase,senthilkumaranb/libcouchbase,avsej/libcouchbase,mody/libcouchbase,PureSwift/libcouchbase,mnunberg/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,mnunberg/libcouchbase,PureSwift/libcouchbase,mnunberg/libcouchbase,mody/libcouchbase,kojiromike/libcouchbase,PureSwift/libcouchbase,PureSwift/libcouchbase,mnunberg/libcouchbase,avsej/libcouchbase