Linux: Set POLLOUT flag for fds to receive XShm completion events

modules/juce_events/native/juce_linux_Messaging.cpp

@@ -111,7 +111,7 @@ public:
         const ScopedLock sl (lock);
 
         fdReadCallbacks.push_back ({ fd, std::move (cb) });
-        pfds.push_back ({ fd, POLLIN, 0 });
+        pfds.push_back ({ fd, POLLIN | POLLOUT, 0 });
     }
 
     void unregisterFdCallback (int fd)

modules/juce_gui_basics/native/juce_linux_X11_Windowing.cpp

@@ -2265,16 +2265,6 @@ private:
         void timerCallback() override
         {
            #if JUCE_USE_XSHM
-            if (XPending (display))
-            {
-                XEvent e;
-
-                ScopedXLock l (display);
-
-                while (XCheckTypedWindowEvent (display, peer.windowH, XShmGetEventBase (display), &e))
-                    --shmPaintsPending;
-            }
-
             if (shmPaintsPending != 0)
                 return;
            #endif