Fix potential js error on summary screen when reloading blocks

[colemanw]

Overview

Fixes a possible edge-case js error on the summary screen when saving and reloading blocks.

Before

Possible error in rare cases where a dependent block has been altered by the layout editor to not support reloading.

After

If clause guards against errors.

[civibot]

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[eileenmcnaughton]

This just adds a precautionary if so seems straight forward. No realistic way to test