fix(gnovm): handle ptr dereferences in ptr to arrays

[thehowl]

Thanks to v01t4ire on hackenproof for the bug report. This fixes a bug whereby slice and range operations on pointers to array could cause an unrecoverable nil pointer dereference. This PR adds the proper nil checks to ensure they create a normal panic, as other cases where we dereference a pointer.

One of the testcases had an issue whereby GetLine would return 0 and cause another panic when generating a stacktrace, so a small fix in machine.go was in order.

[Gno2D2]

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