Bug Fix - blank annotations now disallowed

- Prevented blank annotations from being added, and the description
  being echoed as though it were the annotation applied (thanks to
  Bruce Dillahunty).
- Added bug.annotate.t unit test to prevent regression.

src/command.cpp

@@ -948,6 +948,9 @@ std::string handleColor (Config& conf)
 ////////////////////////////////////////////////////////////////////////////////
 std::string handleAnnotate (TDB& tdb, T& task, Config& conf)
 {
+  if (task.getDescription () == "")
+    throw std::string ("Cannot apply a blank annotation.");
+
   std::stringstream out;
   std::vector <T> all;
   tdb.pendingT (all);