Problem: HWM always boosted by 1

Solution: initialise *hwmboost to -1 instead of 1, and use it only if
it's >= 0. The socket option code checks anyway that the
user-provided value is >= 0 so there is no risk of clashing. The
documentation also specifies that it has to be >= 0.

src/pipe.cpp

@@ -83,8 +83,8 @@ zmq::pipe_t::pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
     out_active (true),
     hwm (outhwm_),
     lwm (compute_lwm (inhwm_)),
-    inhwmboost(1),
-    outhwmboost(1),
+    inhwmboost(-1),
+    outhwmboost(-1),
     msgs_read (0),
     msgs_written (0),
     peers_msgs_read (0),
@@ -508,14 +508,14 @@ void zmq::pipe_t::hiccup ()
 
 void zmq::pipe_t::set_hwms (int inhwm_, int outhwm_)
 {
-    int in = inhwm_ + inhwmboost;
-    int out = outhwm_ + outhwmboost;
+    int in = inhwm_ + (inhwmboost > 0 ? inhwmboost : 0);
+    int out = outhwm_ + (outhwmboost > 0 ? outhwmboost : 0);
 
     // if either send or recv side has hwm <= 0 it means infinite so we should set hwms infinite
-    if (inhwm_ <= 0 || inhwmboost <= 0)
+    if (inhwm_ <= 0 || inhwmboost == 0)
         in = 0;
 
-    if (outhwm_ <= 0 || outhwmboost <= 0)
+    if (outhwm_ <= 0 || outhwmboost == 0)
         out = 0;
 
     lwm = compute_lwm(in);