breaking-change(plugin-svgo): handle potential errors from optimize

[mikaelbr]

Summary

svg.optimize() can in some cases return error, when passed SVG is invalid. There are some cases also, for instance when removing some namespace attributes that the SVG is invalid as a cause of that. When this happens data returned from plugin-svgo will be undefined, causing this to be undefined in the following iteration of the loop. This again causes obscure errors in some cases when running the following plugins.

This depends on fixing the types for svgo: DefinitelyTyped/DefinitelyTyped#58031

Note: Marked this as breaking-change as it explicitly throws an error. There are other ways to handle this (propagate error etc), but feels like showing error here is better than just ignoring it.

This PR does not fix consumers of plugin-svgo to handle error.

Test plan

Added test case to ensure invalid svg throws error.

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[gregberge]

Hello @mikaelbr, I don't think it is a real breaking change here.