GUACAMOLE-1997: Fix issue on screen resize with freerdp >= 3.8.0.

[corentin-soriano]

With freerdp >= 3.8.0, we can't resize with "display-update":

guacd[609180]: DEBUG:   Display update channel will be used for display size changes.
guacd[609180]: DEBUG:   {Microsoft::Windows::RDS::DisplayControl:16} OnOpen=(nil), OnClose=0x7f40b610b150
guacd[609180]: DEBUG:   Server resized display to 768x583
GUAC_ASSERT in guac_rdp_gdi_end_paint() failed at gdi.c:102.
guacd[609080]: INFO:    Connection "$3ec11dae-60d9-4820-9028-01a10f4e95f4" removed.
guacd[609080]: DEBUG:   Unable to request termination of client process: No such process 
guacd[609080]: DEBUG:   All child processes for connection "$3ec11dae-60d9-4820-9028-01a10f4e95f4" have been terminated. 

Caused by this bugfix in freerdp: FreeRDP/FreeRDP#10488
Freerdp triggers EndPaint first when resizing to ensure there are no unfinished BeginPaints.

[mike-jumper]

Freerdp triggers EndPaint first when resizing to ensure there are no unfinished BeginPaints.

I'm a little concerned about that fix in FreeRDP/FreeRDP#10488. Triggering an EndPaint without a corresponding BeginPaint sounds like broken behavior. I see a check in the FreeRDP PR that verifies whether BeginPaint was called, but that check doesn't happen until after EndPaint has been called.

I'll read through the surrounding code on our end a bit deeper, but my main concern is that this change in behavior could cause a race condition in the handling of "Display Update" vs. GDI updates.