Fix the way the module handles errors when no appropriate plugin was found (bad indicator was provided in content)

If user has putted the wrong indicator (have made a typo, which often happens) in content of some fields then the module produce errors.
For example if I put in content the following pattern [[nodetitl:ohaio]] instead of [[nodetitle:ohaio]] then I will end up with the following errors:

Warning: Missing argument 2 for l() in l() (line 2340 of includes/common.inc).
Notice: Undefined variable: path in l() (line 2351 of includes/common.inc).
Notice: Undefined variable: path in l() (line 2351 of includes/common.inc).
Notice: Undefined variable: path in l() (line 2393 of includes/common.inc).

And also module produce not quite nice replacement in text in such situation:
Plugin <em class="placeholder"></em> Not Found