Backends: OpenGL3: Fixed embedded loader multiple init/shutdown cycles broken on some platforms. (#8792, #9112)

backends/imgui_impl_opengl3_loader.h

@@ -836,6 +836,7 @@ static int parse_version(void)
 }
 
 static void load_procs(GL3WGetProcAddressProc proc);
+static void clear_procs();
 
 int imgl3wInit(void)
 {
@@ -855,6 +856,7 @@ int imgl3wInit2(GL3WGetProcAddressProc proc)
 void imgl3wShutdown(void)
 {
     close_libgl();
+    clear_procs();
 }
 
 int imgl3wIsSupported(int major, int minor)
@@ -943,6 +945,13 @@ static void load_procs(GL3WGetProcAddressProc proc)
         imgl3wProcs.ptr[i] = proc(proc_names[i]);
 }
 
+static void clear_procs()
+{
+    size_t i;
+    for (i = 0; i < GL3W_ARRAY_SIZE(proc_names); i++)
+        imgl3wProcs.ptr[i] = nullptr;
+}
+
 #ifdef __cplusplus
 }
 #endif