prevent rclick from bleeding through (again)

docs/changelog.txt

@@ -37,6 +37,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 
 ## Fixes
 - ``Units::isFortControlled``: Account for agitated wildlife
+- Fix right click sometimes closing both a DFHack window and a vanilla panel
 
 ## Misc Improvements
 - `automelt`: is now more resistent to savegame corruption

library/lua/gui.lua

@@ -789,6 +789,7 @@ function ZScreen:onInput(keys)
         end
         if keys._MOUSE_R_DOWN then
             df.global.enabler.mouse_rbut_down = 0
+            df.global.enabler.mouse_rbut = 0
         end
         return
     end