fix rx.image src not working with state

[Lendemor]

Serialization update may have broken the src parameter of rx.image working with State var. (haven't checked if it worked before)

Now work with State var (PIL, absolute link or relative link) or raw values

Closes #1914

[masenf]

I had these examples working a bit ago, do we know what regressed this functionality? https://github.com/masenf/example-pangea

#1619 (comment)

[Lendemor]

I had these examples working a bit ago, do we know what regressed this functionality? https://github.com/masenf/example-pangea

#1619 (comment)

I'm not sure, I didn't dig to find the cause of the regression.
I'm assuming some changes during the serialization changes broke something, need further investigation if we want the exact cause.

[masenf]

It broke in 0.2.8, was working in 0.2.7; Mainly i just want to know if we have a class of bugs that was introduced in that release or if this is a one off problem.

[masenf]

Here is the change that introduced this issue: 1938a6c#diff-4652c902f558b2570fb46d70122cd9bcf9045c7235cebb2c49bd10a8054ace1fL63-R65

Looks like our testing is better now, but we're still missing the case where the src comes from a state Var