fix regression: importing papagayo file didn't show the expected layers

[rodolforg]

Reported-by: BigBang
https://forums.synfig.org/t/no-group-for-the-tones-of-papagayao/12849

fix #1804

guilty commit: f63ade3

Test file: test_pgo.zip

[rodolforg]

The problem exists since 1.3.12 :O

[ice0]

@rodolforg
Can you describe why it didn't work?

[rodolforg]

Can you describe why it didn't work?

The layer parameter value stored and returned by layer->get_params() depends on current layer time set.
Sometimes it is not set yet, and I didn't want to force it.

Looking it again, in the case I added, we don't need to use layer_switch->get_possible_new_layers(possible_new_layers); as we already got them :)

[rodolforg]

Example file (copied from the forums):

lipsync version 1
test-sound.wav
60
243
1
	Voice 1
	that's a test
	1
		that's a test
		34
		110
		3
			that's 34 68 4
				34 etc
				43 AI
				52 etc
				60 etc
			a 69 76 1
				69 AI
			test 77 110 4
				77 etc
				86 E
				94 etc
				103 etc

Edited:
Oh, now I saw I already shared the example file in OP lol

[rodolforg]

Now I avoid the repetition of dynamic_cast() on each (selected) layer parameter.

And there is no need to check the layer_name parameter value(s):

1. layer_switch->get_possible_new_layers(possible_new_layers) already check its values
2. this code slice just shows the possible (and existent) layer children: highlighting what layer is currently selected is done elsewhere (LayerTreeStore::get_value_vfunc()).

[morevnaproject]

Hi! I have finally tested the PR and it works perfectly! Thank you so much!

[morevnaproject]

Backported to 1.4.3.