[perl #131281] next on last iteration of loop injects Mu into return value and fouls termination test

[Brian S. Julin]

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There are some misbehaviors when a next clause is encountered on what would be 
the last iteration of a loop construct.  An extra Mu is injected into the 
return value for that iteration, and the termination test may be bypassed.

skids: m: my $b; (loop ($b = 4; $b; $b--) { next if $b == 1; $_ }).note
(02:05:08 PM) camelia: rakudo-moar 6bb1b5: OUTPUT: «((Any) (Any) (Any) (Mu) 
(Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) 
(Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) 
(Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (Any) (A…»

m: my $b; (loop ($b = 4; $b > 0; $b--) { next if $b == 1; $b }).note # version 
without escaping the termination condition
(02:13:17 PM) camelia: rakudo-moar 6bb1b5: OUTPUT: «(4 3 2 (Mu))␤»
(02:13:25 PM) skids: still have that Mu.