Skip empty calls in the NAME section after the .Nm macro call.

This makes the following difference:

-groff_mdoc(7), -(7)      - groff_mdoc reference for groff's mdoc implementation
+groff_mdoc(7)            - reference for groff's mdoc implementation

gnu/usr.bin/man/makewhatis/makewhatis.perl

@@ -361,6 +361,7 @@ sub manual {
 		last if /^\.Sh/;
 		chop;
 		s/^\.\\".*$//;            #" delete comments
+		next if /^\.[ \t]*$/;	  # skip empty calls
 		if (/^\.Nm/) {
 		    s/^\.Nm[ \t]*//;
 		    s/ ,/,/g;