Auto merge of #2956 - nical:large-rendertask, r=kvark
Auto merge of #2956 - nical:large-rendertask, r=kvark

Add a sanity check for render task sizes

This PR moves the crash happening when failing to allocate large render task textures to the place where the size is assigned in the hope that the stack trace will be more actionable. This will make it easier to investigate #2955.

I'm not sure whether the explicit `panic!()` is needed or if the `error!()` macro already panics.

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