check if the uv_poll_t struct is initialized before calling uv_poll_stop

Before this fix a call to End after an error in Connect() would result in
a segfault.

brianc#136 (comment)

Author: booo

src/binding.cc

@@ -234,13 +234,14 @@ class Connection : public ObjectWrap {
 
   uv_poll_t read_watcher_;
   uv_poll_t  write_watcher_;
-
   PGconn *connection_;
   bool connecting_;
+  bool ioInitialized_;
   Connection () : ObjectWrap ()
   {
     connection_ = NULL;
     connecting_ = false;
+    ioInitialized_ = false;
 
     TRACE("Initializing ev watchers");
     read_watcher_.data = this;
@@ -354,6 +355,8 @@ class Connection : public ObjectWrap {
     uv_poll_init(uv_default_loop(), &read_watcher_, fd);
     uv_poll_init(uv_default_loop(), &write_watcher_, fd);
 
+    ioInitialized_ = true;
+
     connecting_ = true;
     StartWrite();
 
@@ -616,7 +619,9 @@ class Connection : public ObjectWrap {
   void StopWrite()
   {
     TRACE("Stoping write watcher");
-    uv_poll_stop(&write_watcher_);
+    if(ioInitialized_) {
+      uv_poll_stop(&write_watcher_);
+    }
   }
 
   void StartWrite()
@@ -628,7 +633,9 @@ class Connection : public ObjectWrap {
   void StopRead()
   {
     TRACE("Stoping read watcher");
-    uv_poll_stop(&read_watcher_);
+    if(ioInitialized_) {
+      uv_poll_stop(&read_watcher_);
+    }
   }
 
   void StartRead()