Midi: fix SysEx handling

We need to clear the event status after each message. Otherwise, after a SysEx message the first byte of the next event will incorrectly inherit its delta_time.
This causes a delay of several seconds in nearly every MT-32 games which uses a lot of long SysEx.

retroarch.c

@@ -14734,6 +14734,8 @@ bool midi_driver_write(uint8_t byte, uint32_t delta_time)
 #endif
 
       midi_drv_output_pending             = true;
+      midi_drv_output_event.data_size     = 0;
+      midi_drv_output_event.delta_time    = 0;
    }
 
    return true;