Reject protover extra commas in protover

Like how it handles spaces, protover.c rejects leading commas (Link=,1-5 or Link=,) while it accepts and ignores extra commas elsewhere (Link=1-5, and Link=1,,,2-5 are valid).

The Rust version accepts and ignores all extra commas, including leading commas.

Trac:
Username: cyberpunks

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