bricks/main: handle pending events before user program

Changes in how the HMI works requires that we handle events before
starting the user program, otherwise the user program start event
handlers will not run until after the user program has started which
leads to race conditions with control of the hub lights.

Fixes: pybricks/pybricks-micropython#13

Author: dlech

bricks/nxt/main.c

@@ -85,6 +85,9 @@ int main(int argc, char **argv) {
 
     // Get system hardware ready
     pbsys_prepare_user_program(&user_program_callbacks);
+    // make sure any pending events are handled before starting MicroPython
+    while (pbio_do_one_event()) {
+    }
 
     // Initialize MicroPython and run default imports
     mp_init();

bricks/stm32/main.c

@@ -286,6 +286,10 @@ int main(int argc, char **argv) {
 
     // Get system hardware ready
     pbsys_prepare_user_program(&user_program_callbacks);
+    // make sure any pending events are handled before starting MicroPython
+    while (pbio_do_one_event()) {
+    }
+
     mp_init();
 
     // Execute the user script