X11: Fix IM-duplicated key events leaking through

Fixes #747.
Fixes #964.

README.md

@@ -173,6 +173,7 @@ information on what to include when reporting a bug.
 - [X11] Bugfix: Window creation on 64-bit would read past top of stack (#951)
 - [X11] Bugfix: XDND support had multiple non-conformance issues (#968)
 - [X11] Bugfix: The RandR monitor path was disabled despite working RandR (#972)
+- [X11] Bugfix: IM-duplicated key events would leak at low polling rates (#747)
 - [Linux] Bugfix: Event processing did not detect joystick disconnection (#932)
 - [Cocoa] Added support for Vulkan window surface creation via
           [MoltenVK](https://moltengl.com/moltenvk/) (#870)

src/x11_platform.h

@@ -141,8 +141,7 @@ typedef struct _GLFWwindowX11
     // The last position the cursor was warped to by GLFW
     int             warpCursorPosX, warpCursorPosY;
 
-    // The information from the last KeyPress event
-    unsigned int    lastKeyCode;
+    // The time of the last KeyPress event
     Time            lastKeyTime;
 
 } _GLFWwindowX11;

src/x11_window.c

@@ -992,17 +992,16 @@ static void processEvent(XEvent *event)
             if (window->x11.ic)
             {
                 // HACK: Ignore duplicate key press events generated by ibus
-                //       Corresponding release events are filtered out by the
-                //       GLFW key repeat logic
-                if (window->x11.lastKeyCode != keycode ||
-                    window->x11.lastKeyTime != event->xkey.time)
+                //       These have the same timestamp as the original event
+                //       Corresponding release events are filtered out
+                //       implicitly by the GLFW key repeat logic
+                if (window->x11.lastKeyTime < event->xkey.time)
                 {
                     if (keycode)
                         _glfwInputKey(window, key, keycode, GLFW_PRESS, mods);
-                }
 
-                window->x11.lastKeyCode = keycode;
                     window->x11.lastKeyTime = event->xkey.time;
+                }
 
                 if (!filtered)
                 {