HoI 4 - Supply checks for volunteers use inconsistent source

[bitmode]

Description of issue
Supply checks for volunteers use inconsistent source

Game Version
1.8.1

Enabled DLC
Together for Victory

Do you have mods enabled?
no

Description
Volunteers are supplied from and by their origin country but they can be cut off if no trade delivery route between the sending and receiving countries' capitals exists. So despite having a valid supply route originating from the sending capital, their reinforcements will be blocked.
Examples of this include communist volunteers in Spain, when Republican Spain loses majority control of La Mancha (very frequent), or a communist minor sending volunteers to the PRC, where the land-based trade route is too long but a naval supply route (through National China) exists.

Steps to Reproduce

• start as SPR
• disable ai
• trigger event spain.1
• select Republicans
• tag D01
• occupationpaint Ciudad Real and Cuenca
• tag SAF
• add_party_popularity communism 10
• Focus.AutoComplete
• Complete Abandon Westminster, Empower the Workers, Support Spain
• select "Perhaps a few of our soldiers [...]"
• offer volunteers to SPR
• tag SPR
• accept offer
• hover one of the volunteers in the division list, their reinforcement are blocked
• recapture Ciudad Real and Cuenca
• let one game hour pass
• the reinforcement is not blocked anymore