Handle empty text masks.

This allows themes to prevent text from being sent during password
entry. To enable, edit theme.hjson and set $.customization.defaults
.general.passwordChar to "". e.g.,

{
  ...
  customization: {
    defaults: {
      general: {
        passwordChar: ""
      }
    }
    ...
  }
}

core/edit_text_view.js

@@ -68,8 +68,9 @@ EditTextView.prototype.onKeyPress = function(ch, key) {
 			} else {
 				this.cursorPos.col += 1;
 
-				if(this.textMaskChar) {
-					this.client.term.write(this.textMaskChar);
+				if(_.isString(this.textMaskChar)) {
+					if(this.textMaskChar.length > 0)
+						this.client.term.write(this.textMaskChar);
 				} else {
 					this.client.term.write(ch);
 				}