Bug Fix - parsing

- Now properly enumerates ambiguous commands.
- Now properly enumerates ambiguous colors.
- Now displays suitable error when a command like "task x" is entered.

src/Context.cpp

@@ -550,7 +550,14 @@ void Context::parse (
     parseTask.set ("description", descCandidate);
   }
 
-  // TODO task.validate () ?
+  // At this point, either a sequence or a command should have been found.
+  if (parseSequence.size () == 0 && parseCmd.command == "")
+  {
+    parseCmd.parse (descCandidate);
+    throw stringtable.get (
+      CMD_MISSING,
+      "You must specify a command, or a task ID to modify");
+  }
 
   // Read-only command (reports, status, info ...) use filters.  Write commands
   // (add, done ...) do not.