Fix LT-22523: Make user aware when Run Tests does nothing (#895)

Author: jtmaxwell3

Src/LexText/ParserUI/ParserListener.cs

@@ -586,6 +586,15 @@ public bool OnCheckParserOnCurrentText(object argument)
 			return true;    //we handled this.
 		}
 
+		public bool OnDisplayCheckParserOnCurrentText(object commandObject, ref UIItemDisplayProperties display)
+		{
+			CheckDisposed();
+
+			display.Enabled = CurrentText != null;
+
+			return true;    //we handled this.
+		}
+
 		public bool OnCheckParserOnGenre(object argument)
 		{
 			CheckDisposed();