Handle events without contract IDs correctly

[Shaptic]

As reported on Discord and confirmed by an example in the docs, the SorobanRpc.Server.getEvents method will fail when the event response contains an empty contract ID. There was an implicit assumption in the code that it would always be present and valid, but in fact it can sometimes be empty.

This modifies the parseRawEvents code to omit the contractId field from the parsed response.

[github-actions]

Size Change: +4.39 kB (0%)

Total Size: 12.1 MB

Filename	Size	Change
dist/stellar-sdk.js	6.96 MB	+3.02 kB (0%)
dist/stellar-sdk.min.js	5.1 MB	+1.37 kB (0%)

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