Bad codegen with ,= meta op

[zoffixznet]

Looks like some cases gen assign instead of p6store op, which causes errors to be thrown:

https://irclog.perlgeek.de/perl6/2018-05-31#i_16229415

14:48 	Zoffix 	m: say [] ,= 42
14:48 	camelia 	rakudo-moar c80ea2f28: OUTPUT: «Cannot assign to an immutable value␤  in block <unit> at <tmp> line 1␤␤»
14:48 	Zoffix 	What immutable value?
14:49 	moritz 	m: [] = 42
14:49 	camelia 	rakudo-moar c80ea2f28: ( no output )
14:50 	moritz 	m: [] = [], 42
14:50 	camelia 	rakudo-moar c80ea2f28: ( no output )
14:50 	moritz 	looks like a bug to me


14:50 	Zoffix 	Yeah, looks like the genned QAST uses assign instead p6store op



14:51 		m: my @a; my @b; @a ,= @b
14:51 	camelia 	rakudo-moar c80ea2f28: ( no output )
14:51 	Zoffix 	m: my @a; my @b; @a [R,]= @b
14:51 	camelia 	rakudo-moar c80ea2f28: OUTPUT: «Cannot assign to an immutable value␤  in block <unit> at <tmp> line 1␤␤»

[dogbert17]

As per b9b0838 it no longer crashes. Fixed?