Fix vertical position of Comms Relay textbox

Fixes #1242.

Turns out it was a really simple fix - the X positions were good, but
the Y positions were always at the top of the screen regardless of the
height of the textbox. Now they're vertically centered respective to
the speaker.

desktop_version/src/Graphics.cpp

@@ -3402,6 +3402,7 @@ static void commsrelay_textbox(textboxclass* THIS)
     THIS->wrap(11);
     THIS->resize();
     THIS->xp = 224 - THIS->w;
+    THIS->yp = 32 - THIS->h/2;
 }
 
 void Graphics::textboxcommsrelay(const char* text)