Term should return error on unsupported systems

Fixes #1494

internal/action/command.go

@@ -807,6 +807,11 @@ func (h *BufPane) ReplaceAllCmd(args []string) {
 func (h *BufPane) TermCmd(args []string) {
 	ps := h.tab.Panes
 
+	if !TermEmuSupported {
+		InfoBar.Error("Terminal emulator not supported on this system")
+		return
+	}
+
 	if len(args) == 0 {
 		sh := os.Getenv("SHELL")
 		if sh == "" {
@@ -830,7 +835,12 @@ func (h *BufPane) TermCmd(args []string) {
 		}
 
 		v := h.GetView()
-		MainTab().Panes[i] = NewTermPane(v.X, v.Y, v.Width, v.Height, t, id, MainTab())
+		tp, err := NewTermPane(v.X, v.Y, v.Width, v.Height, t, id, MainTab())
+		if err != nil {
+			InfoBar.Error(err)
+			return
+		}
+		MainTab().Panes[i] = tp
 		MainTab().SetActive(i)
 	}
 

internal/action/terminal_supported.go

@@ -30,7 +30,12 @@ func RunTermEmulator(h *BufPane, input string, wait bool, getOutput bool, callba
 	id := MainTab().Panes[0].ID()
 
 	v := h.GetView()
-	MainTab().Panes[0] = NewTermPane(v.X, v.Y, v.Width, v.Height, t, id, MainTab())
+
+	tp, err := NewTermPane(v.X, v.Y, v.Width, v.Height, t, id, MainTab())
+	if err != nil {
+		return err
+	}
+	MainTab().Panes[0] = tp
 	MainTab().SetActive(0)
 
 	return nil

internal/action/termpane.go

@@ -1,6 +1,7 @@
 package action
 
 import (
+	"errors"
 	"runtime"
 
 	"github.com/zyedidia/clipboard"
@@ -20,14 +21,18 @@ type TermPane struct {
 	tab           *Tab
 }
 
-func NewTermPane(x, y, w, h int, t *shell.Terminal, id uint64, tab *Tab) *TermPane {
+func NewTermPane(x, y, w, h int, t *shell.Terminal, id uint64, tab *Tab) (*TermPane, error) {
+	if !TermEmuSupported {
+		return nil, errors.New("Terminal emulator is not supported on this system")
+	}
+
 	th := new(TermPane)
 	th.Terminal = t
 	th.id = id
 	th.mouseReleased = true
 	th.Window = display.NewTermWindow(x, y, w, h, t)
 	th.tab = tab
-	return th
+	return th, nil
 }
 
 func (t *TermPane) ID() uint64 {