GLX: Fix context creation failing unnecessarily

Regression introduced with 3bb5c459d6.

(cherry picked from commit 2e656afc49)

README.md

@@ -135,6 +135,7 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: Full screen window creation did not ignore `GLFW_VISIBLE`
  - [Wayland] Bugfix: Some keys were reported as wrong key or `GLFW_KEY_UNKNOWN`
  - [Wayland] Bugfix: Text input did not repeat along with key repeat
+ - [GLX] Bugfix: Context creation failed if GLX 1.4 was not exported by GLX library
 
 
 ## Contact

src/glx_context.c

@@ -309,10 +309,6 @@ GLFWbool _glfwInitGLX(void)
         _glfw_dlsym(_glfw.glx.handle, "glXCreateWindow");
     _glfw.glx.DestroyWindow =
         _glfw_dlsym(_glfw.glx.handle, "glXDestroyWindow");
-    _glfw.glx.GetProcAddress =
-        _glfw_dlsym(_glfw.glx.handle, "glXGetProcAddress");
-    _glfw.glx.GetProcAddressARB =
-        _glfw_dlsym(_glfw.glx.handle, "glXGetProcAddressARB");
     _glfw.glx.GetVisualFromFBConfig =
         _glfw_dlsym(_glfw.glx.handle, "glXGetVisualFromFBConfig");
 
@@ -328,8 +324,6 @@ GLFWbool _glfwInitGLX(void)
         !_glfw.glx.CreateNewContext ||
         !_glfw.glx.CreateWindow ||
         !_glfw.glx.DestroyWindow ||
-        !_glfw.glx.GetProcAddress ||
-        !_glfw.glx.GetProcAddressARB ||
         !_glfw.glx.GetVisualFromFBConfig)
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
@@ -337,6 +331,12 @@ GLFWbool _glfwInitGLX(void)
         return GLFW_FALSE;
     }
 
+    // NOTE: Unlike GLX 1.3 entry points these are not required to be present
+    _glfw.glx.GetProcAddress = (PFNGLXGETPROCADDRESSPROC)
+        _glfw_dlsym(_glfw.glx.handle, "glXGetProcAddress");
+    _glfw.glx.GetProcAddressARB = (PFNGLXGETPROCADDRESSPROC)
+        _glfw_dlsym(_glfw.glx.handle, "glXGetProcAddressARB");
+
     if (!glXQueryExtension(_glfw.x11.display,
                            &_glfw.glx.errorBase,
                            &_glfw.glx.eventBase))