regen/embed.pl: Add a condition to an 'if'

$argname is used inside this 'if' as part of a newly created array
element.  It needs to be defined for the code to work that later looks
at that element.

No current calls result in an undefined value for this.

Author: khwilliamson

regen/embed.pl

@@ -274,7 +274,12 @@ sub generate_proto_h {
                     die_at_end "$func: $arg ($n) doesn't have a name\n";
                 }
                 my $argname = $1;
-                if (!$nocheck and defined $argtype and exists $type_asserts{$argtype}) {
+
+                if (    defined $argname
+                    and ! $nocheck
+                    and defined $argtype
+                    and exists $type_asserts{$argtype})
+                {
                     push @typed_args, [ $argtype, $argname ];
                 }