Minor refactoring tcell library from tui.go to tcell.go

To prevent including tcell library in non-windows builds.

src/tui/tcell.go

@@ -120,8 +120,11 @@ func (a Attr) Merge(b Attr) Attr {
 	return a | b
 }
 
+// handle the following as private members of FullscreenRenderer instance
+// they are declared here to prevent introducing tcell library in non-windows builds
 var (
 	_screen          tcell.Screen
+	_prevMouseButton tcell.ButtonMask
 )
 
 func (r *FullscreenRenderer) initScreen() {
@@ -193,8 +196,8 @@ func (r *FullscreenRenderer) GetChar() Event {
 		mod := ev.Modifiers() != 0
 
 		// since we dont have mouse down events (unlike LightRenderer), we need to track state in prevButton
-		prevButton, button := r.prevMouseButton, ev.Buttons()
+		prevButton, button := _prevMouseButton, ev.Buttons()
-		r.prevMouseButton = button
+		_prevMouseButton = button
 		drag := prevButton == button
 
 		switch {

src/tui/tui.go

@@ -5,8 +5,6 @@ import (
 	"os"
 	"strconv"
 	"time"
-
-	"github.com/gdamore/tcell"
 )
 
 // Types of user action
@@ -403,7 +401,6 @@ type FullscreenRenderer struct {
 	mouse        bool
 	forceBlack   bool
 	prevDownTime time.Time
-	prevMouseButton tcell.ButtonMask
 	clickY       []int
 }
 
@@ -413,7 +410,6 @@ func NewFullscreenRenderer(theme *ColorTheme, forceBlack bool, mouse bool) Rende
 		mouse:        mouse,
 		forceBlack:   forceBlack,
 		prevDownTime: time.Unix(0, 0),
-		prevMouseButton: tcell.ButtonNone,
 		clickY:       []int{}}
 	return r
 }