Missing mass_breakdown_sun_plot when using low rtol solver values

[enricostragiotti]

Describe the bug
The plotting function mass_breakdown_sun_plot produces a single plot (only the OWE breakdown) if MTOW != OWE + payload + onboard_fuel_at_takeoff.

See image:

To Reproduce
When solving a simple MDA specifying a low acceptable rtol e.g. nonlinear_solver: om.NonlinearBlockGS(maxiter=100, rtol=1e-2) it can happen that MTOW != OWE + payload + onboard_fuel_at_takeoff. In those cases the following test

FAST-OAD/src/fastoad/gui/analysis_and_plots.py

Lines 371 to 372 in 50bc36a

	if round(mtow, 6) == round(owe + payload + onboard_fuel_at_takeoff, 6):
	mtow = owe + payload + onboard_fuel_at_takeoff

is not passed and the image is not generated.

Expected behavior
A user feedback explaining what is happening could be beneficial, as "The MTOW breakdown is not plotted as MTOW / (OWE + payload + onboard_fuel_at_takeoff) is higher than ... Try to re-run the MDA with a lower solver rtol value."

Environment

• Operating System: Windows 10
• Python environment: Python 3.9.13