terminal: do not crash when process exits during next

Fixes #1090

pkg/terminal/command_test.go

@@ -717,3 +717,18 @@ func TestDisassembleAutogenerated(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue1090(t *testing.T) {
+	// Exit while executing 'next' should report the "Process exited" error
+	// message instead of crashing.
+	withTestTerminal("math", t, func(term *FakeTerminal) {
+		term.MustExec("break main.main")
+		term.MustExec("continue")
+		for {
+			_, err := term.Exec("next")
+			if err != nil && strings.Contains(err.Error(), " has exited with status ") {
+				break
+			}
+		}
+	})
+}