Fix: Mex building deselection in default buildmenu (#2654)

luaui/Widgets/cmd_extractor_snap.lua

@@ -11,6 +11,7 @@ function widget:GetInfo()
 	}
 end
 
+include("keysym.h.lua")
 
 local spGetActiveCommand = Spring.GetActiveCommand
 local spGetMouseState = Spring.GetMouseState
@@ -252,9 +253,15 @@ end
 
 
 -- Since mex snap bypasses normal building behavior, we have to hand hold gridmenu a little bit
+local endShift = false
 local function handleBuildMenu(shift)
 	local grid = WG["gridmenu"]
 	if not grid or not grid.clearCategory or not grid.getAlwaysReturn or not grid.setCurrentCategory then
+		if not shift then
+			Spring.SetActiveCommand(0)
+		else
+			endShift = true
+		end
 		return
 	end
 
@@ -287,6 +294,14 @@ function widget:MousePress(x, y, button)
 end
 
 
+-- I really hate that I have to do this, but something is hardcoding shift behavior with mouse clicks, and I need to override it
+function widget:KeyRelease(code)
+	if endShift and (code == KEYSYMS.LSHIFT or code == KEYSYMS.RSHIFT) then
+		Spring.SetActiveCommand(0)
+	end
+end
+
+
 function widget:DrawWorld()
 	if not WG.DrawUnitShapeGL4
 	or not targetPos