[grblHAL/STM32F4xx Issue#127] HardFault when stepper segment buffer is empty

Running a Blackpill STM32F411CE. Driving a galvo with a adc using code from stmorpodac.c.
In this setup I can have very high feedrate and while testing how far I can go i run into a hardfault when stepper segment buffer become empty when there is lot of short segments i gcode file.
Running in laser_mode.

The crash is in this code, grbl/stepper.c
>ISRCODE void ISRFUNC(stepperdriverinterrupt_handler)(void)
{
….
// Segment buffer empty. Shutdown.
stgoidle();
// Ensure pwm is set properly upon completion of rate-controlled motion.
if (st.execblock->dynamicrpm && st.exec_block->spindle->cap.laser)
st.execblock->spindle->updatepwm(st.execblock->spindle->pwmoff_value);

I put a breakpoint at the stgoidle() row.
Second time breakpoint hits st.exec_block is null.
The st struct looks like this when it crashes
>B::Var.View_%Recursive%open_st
st = (
counter_x = 52520,
counter_y = 107472,
counter_z = 107472,
counter_a = 107472,
counter_b = 107472,
new_block = FALSE,
dir_change = FALSE,
step_outbits = (mask = 2, value = 2, x = 0, y = 1, z = 0, a = 0, b = 0, c = 0, u = 0, v = 0),
dir_outbits = (mask = 1, value = 1, x = 1, y = 0, z = 0, a = 0, b = 0, c = 0, u = 0, v = 0),
steps = (8, 214944, 0, 0, 0),
amass_level = 0,
step_count = 0,
stepeventcount = 214944,
exec_block = 0x0 -> NULL,
exec_segment = 0x0 -> NULL)

First time breakpoint hit (when it not crashes) st looks like this
>B::Var.View_%Recursive%open_st
st = (
counter_x = 52520,
counter_y = 107472,
counter_z = 107472,
counter_a = 107472,
counter_b = 107472,
new_block = FALSE,
dir_change = FALSE,
step_outbits = (mask = 2, value = 2, x = 0, y = 1, z = 0, a = 0, b = 0, c = 0, u = 0, v = 0),
dir_outbits = (mask = 1, value = 1, x = 1, y = 0, z = 0, a = 0, b = 0, c = 0, u = 0, v = 0),
steps = (8, 214944, 0, 0, 0),
amass_level = 0,
step_count = 0,
stepeventcount = 214944,
execblock = 0x2000115C -> (id = 2, next = 0x2000119C, steps = (8, 214944, 0, 0, 0), stepeventcount = 214944, directionbits = (mask = 1, value = 1, x = 1, y = 0, z = 0, a = 0, b = 0, c = 0, u = 0, v = 0), overrides = (value = 0, feedratedisable = 0, feedholddisable = 0, spindlerpmdisable = 0, parkingdisable = 0, reserved = 0, sync = 0), stepspermm = 600.0, millimeters = 44.779999, programmedrate = 50000.0, message = 0x0, outputcommands = 0x0, backlashmotion = FALSE, dynamic_rpm = FALSE, spindle = 0x20000DA8),
exec_segment = 0x0 -> NULL)